boards/native: set PORT to tap0
boards/native: set PORT to tap0

`PORT` is unset if `netdev2_tap` is not in `USEMODULES`.
But unfortunately, `netdev2_tap` is set by boards/native/Makefile.dep
*after* `PORT` is set, so that `PORT` remains empty.

This commit breaks this circular dependency by checking for
`netdev_default` and `gnrc_netdev_default` instead.

Without this commit, `make term` throws an error for examples that
require a tap interface, when `PORT` is not explicitely given.

jasonatran/RIOT,LudwigKnuepfer/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,backenklee/RIOT,katezilla/RIOT,tfar/RIOT,LudwigOrtmann/RIOT,gautric/RIOT,Josar/RIOT,authmillenon/RIOT,dkm/RIOT,avmelnikoff/RIOT,jasonatran/RIOT,biboc/RIOT,kerneltask/RIOT,aeneby/RIOT,katezilla/RIOT,josephnoir/RIOT,miri64/RIOT,jfischer-phytec-iot/RIOT,kb2ma/RIOT,kaleb-himes/RIOT,aeneby/RIOT,yogo1212/RIOT,kerneltask/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kb2ma/RIOT,immesys/RiSyn,yogo1212/RIOT,miri64/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,OlegHahm/RIOT,LudwigKnuepfer/RIOT,immesys/RiSyn,immesys/RiSyn,immesys/RiSyn,kaleb-himes/RIOT,LudwigOrtmann/RIOT,roberthartung/RIOT,gebart/RIOT,Josar/RIOT,A-Paul/RIOT,biboc/RIOT,Hyungsin/RIOT-OS,avmelnikoff/RIOT,kbumsik/RIOT,TobiasFredersdorf/RIOT,Josar/RIOT,adjih/RIOT,jasonatran/RIOT,hamilton-mote/RIOT-OS,thomaseichinger/RIOT,backenklee/RIOT,neumodisch/RIOT,yogo1212/RIOT,aeneby/RIOT,syin2/RIOT,ks156/RIOT,neiljay/RIOT,gautric/RIOT,josephnoir/RIOT,syin2/RIOT,lazytech-org/RIOT,adrianghc/RIOT,hamilton-mote/RIOT-OS,avmelnikoff/RIOT,ks156/RIOT,Ell-i/RIOT,thomaseichinger/RIOT,gautric/RIOT,jbeyerstedt/RIOT-OTA-update,beurdouche/RIOT,gautric/RIOT,beurdouche/RIOT,tfar/RIOT,adjih/RIOT,basilfx/RIOT,thomaseichinger/RIOT,dkm/RIOT,basilfx/RIOT,adrianghc/RIOT,hamilton-mote/RIOT-OS,jbeyerstedt/RIOT-OTA-update,thomaseichinger/RIOT,kaspar030/RIOT,backenklee/RIOT,basilfx/RIOT,neumodisch/RIOT,miri64/RIOT,neiljay/RIOT,gautric/RIOT,ks156/RIOT,authmillenon/RIOT,OlegHahm/RIOT,TobiasFredersdorf/RIOT,katezilla/RIOT,miri64/RIOT,cladmi/RIOT,toonst/RIOT,katezilla/RIOT,smlng/RIOT,dkm/RIOT,BytesGalore/RIOT,kYc0o/RIOT,aeneby/RIOT,gebart/RIOT,adrianghc/RIOT,x3ro/RIOT,A-Paul/RIOT,BytesGalore/RIOT,cladmi/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,kerneltask/RIOT,authmillenon/RIOT,jfischer-phytec-iot/RIOT,TobiasFredersdorf/RIOT,yogo1212/RIOT,mfrey/RIOT,avmelnikoff/RIOT,immesys/RiSyn,Ell-i/RIOT,alignan/RIOT,neiljay/RIOT,miri64/RIOT,lazytech-org/RIOT,kYc0o/RIOT,x3ro/RIOT,josephnoir/RIOT,backenklee/RIOT,ks156/RIOT,alignan/RIOT,kb2ma/RIOT,neumodisch/RIOT,Hyungsin/RIOT-OS,biboc/RIOT,plushvoxel/RIOT,ant9000/RIOT,Ell-i/RIOT,lazytech-org/RIOT,kerneltask/RIOT,neiljay/RIOT,kaspar030/RIOT,thomaseichinger/RIOT,Hyungsin/RIOT-OS,beurdouche/RIOT,ks156/RIOT,tfar/RIOT,toonst/RIOT,jfischer-phytec-iot/RIOT,hamilton-mote/RIOT-OS,neumodisch/RIOT,smlng/RIOT,biboc/RIOT,kaleb-himes/RIOT,A-Paul/RIOT,mfrey/RIOT,syin2/RIOT,x3ro/RIOT,Hyungsin/RIOT-OS,kYc0o/RIOT,rfuentess/RIOT,neumodisch/RIOT,mtausig/RIOT,roberthartung/RIOT,TobiasFredersdorf/RIOT,OTAkeys/RIOT,kbumsik/RIOT,dailab/RIOT,plushvoxel/RIOT,toonst/RIOT,roberthartung/RIOT,kbumsik/RIOT,RIOT-OS/RIOT,dailab/RIOT,LudwigOrtmann/RIOT,kb2ma/RIOT,A-Paul/RIOT,OTAkeys/RIOT,ant9000/RIOT,BytesGalore/RIOT,yogo1212/RIOT,toonst/RIOT,LudwigOrtmann/RIOT,cladmi/RIOT,jbeyerstedt/RIOT-OTA-update,OlegHahm/RIOT,RIOT-OS/RIOT,LudwigKnuepfer/RIOT,jasonatran/RIOT,kb2ma/RIOT,lazytech-org/RIOT,mfrey/RIOT,LudwigKnuepfer/RIOT,tfar/RIOT,adjih/RIOT,josephnoir/RIOT,x3ro/RIOT,rfuentess/RIOT,OlegHahm/RIOT,roberthartung/RIOT,backenklee/RIOT,neiljay/RIOT,LudwigOrtmann/RIOT,LudwigKnuepfer/RIOT,toonst/RIOT,adjih/RIOT,Ell-i/RIOT,RIOT-OS/RIOT,ant9000/RIOT,mfrey/RIOT,beurdouche/RIOT,cladmi/RIOT,mtausig/RIOT,roberthartung/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,mtausig/RIOT,OlegHahm/RIOT,mtausig/RIOT,jbeyerstedt/RIOT-OTA-update,katezilla/RIOT,smlng/RIOT,kaspar030/RIOT,kaspar030/RIOT,plushvoxel/RIOT,syin2/RIOT,immesys/RiSyn,basilfx/RIOT,kbumsik/RIOT,gebart/RIOT,jasonatran/RIOT,neumodisch/RIOT,authmillenon/RIOT,adjih/RIOT,smlng/RIOT,authmillenon/RIOT,kaleb-himes/RIOT,alignan/RIOT,mfrey/RIOT,authmillenon/RIOT,smlng/RIOT,Josar/RIOT,kYc0o/RIOT,lazytech-org/RIOT,biboc/RIOT,OTAkeys/RIOT,dailab/RIOT,rfuentess/RIOT,avmelnikoff/RIOT,syin2/RIOT,A-Paul/RIOT,adrianghc/RIOT,BytesGalore/RIOT,OTAkeys/RIOT,cladmi/RIOT,OTAkeys/RIOT,adrianghc/RIOT,RIOT-OS/RIOT,BytesGalore/RIOT,jfischer-phytec-iot/RIOT,aeneby/RIOT,tfar/RIOT,dailab/RIOT,rfuentess/RIOT,basilfx/RIOT,kaspar030/RIOT,beurdouche/RIOT,mtausig/RIOT,rfuentess/RIOT,LudwigOrtmann/RIOT,alignan/RIOT,gebart/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,kbumsik/RIOT,ant9000/RIOT,dkm/RIOT,plushvoxel/RIOT,yogo1212/RIOT,Josar/RIOT,ant9000/RIOT,x3ro/RIOT,plushvoxel/RIOT,jfischer-phytec-iot/RIOT,Hyungsin/RIOT-OS,kerneltask/RIOT,kaleb-himes/RIOT,gebart/RIOT,hamilton-mote/RIOT-OS,dailab/RIOT,Ell-i/RIOT,TobiasFredersdorf/RIOT,josephnoir/RIOT,jbeyerstedt/RIOT-OTA-update,alignan/RIOT,dkm/RIOT