gnrc_ipv6: discard non-NONXT packets with 0 payload length
gnrc_ipv6: discard non-NONXT packets with 0 payload length

If the payload length is zero and the next header field is not set to
NONXT, GNRC will interpret the current header as the payload because the
first snip is always interpreted as the payload. This can lead to loops
and or crashes.

avmelnikoff/RIOT,lazytech-org/RIOT,aeneby/RIOT,jasonatran/RIOT,rfuentess/RIOT,jasonatran/RIOT,kaspar030/RIOT,OlegHahm/RIOT,toonst/RIOT,kYc0o/RIOT,josephnoir/RIOT,mfrey/RIOT,x3ro/RIOT,kYc0o/RIOT,yogo1212/RIOT,basilfx/RIOT,mtausig/RIOT,authmillenon/RIOT,yogo1212/RIOT,mtausig/RIOT,kYc0o/RIOT,cladmi/RIOT,basilfx/RIOT,miri64/RIOT,rfuentess/RIOT,cladmi/RIOT,miri64/RIOT,biboc/RIOT,rfuentess/RIOT,cladmi/RIOT,OlegHahm/RIOT,A-Paul/RIOT,RIOT-OS/RIOT,smlng/RIOT,OlegHahm/RIOT,basilfx/RIOT,OlegHahm/RIOT,BytesGalore/RIOT,kbumsik/RIOT,kbumsik/RIOT,kaspar030/RIOT,x3ro/RIOT,smlng/RIOT,smlng/RIOT,OTAkeys/RIOT,authmillenon/RIOT,A-Paul/RIOT,gebart/RIOT,authmillenon/RIOT,avmelnikoff/RIOT,smlng/RIOT,kYc0o/RIOT,cladmi/RIOT,aeneby/RIOT,kbumsik/RIOT,basilfx/RIOT,basilfx/RIOT,jasonatran/RIOT,OTAkeys/RIOT,ant9000/RIOT,cladmi/RIOT,yogo1212/RIOT,BytesGalore/RIOT,authmillenon/RIOT,OTAkeys/RIOT,neiljay/RIOT,yogo1212/RIOT,authmillenon/RIOT,kaspar030/RIOT,kbumsik/RIOT,A-Paul/RIOT,kYc0o/RIOT,toonst/RIOT,A-Paul/RIOT,avmelnikoff/RIOT,biboc/RIOT,lazytech-org/RIOT,RIOT-OS/RIOT,biboc/RIOT,x3ro/RIOT,jasonatran/RIOT,mtausig/RIOT,rfuentess/RIOT,biboc/RIOT,toonst/RIOT,A-Paul/RIOT,mtausig/RIOT,mtausig/RIOT,lazytech-org/RIOT,authmillenon/RIOT,neiljay/RIOT,gebart/RIOT,aeneby/RIOT,BytesGalore/RIOT,neiljay/RIOT,josephnoir/RIOT,kbumsik/RIOT,miri64/RIOT,ant9000/RIOT,biboc/RIOT,aeneby/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,x3ro/RIOT,miri64/RIOT,josephnoir/RIOT,gebart/RIOT,mfrey/RIOT,lazytech-org/RIOT,yogo1212/RIOT,ant9000/RIOT,lazytech-org/RIOT,kaspar030/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,BytesGalore/RIOT,BytesGalore/RIOT,mfrey/RIOT,kaspar030/RIOT,toonst/RIOT,gebart/RIOT,avmelnikoff/RIOT,avmelnikoff/RIOT,smlng/RIOT,ant9000/RIOT,mfrey/RIOT,rfuentess/RIOT,ant9000/RIOT,x3ro/RIOT,neiljay/RIOT,RIOT-OS/RIOT,mfrey/RIOT,josephnoir/RIOT,toonst/RIOT,yogo1212/RIOT,miri64/RIOT,aeneby/RIOT,OlegHahm/RIOT,neiljay/RIOT,josephnoir/RIOT,gebart/RIOT