kw2xrf: set tx_power in gnrc_netdev_t
kw2xrf: set tx_power in gnrc_netdev_t

without this patch, tx_power is directly set on the device but not in
gnrc_netdev_t. Thus, calling ifconfig in shell shows tx_power always
at 0dBm, never showing the correct, current value. Additionally, it
verifies that given tx_power to be set is in valid range.

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