gnrc_ipv6_nib: release when not queuable on AR
gnrc_ipv6_nib: release when not queuable on AR

When a new queue entry is tried to be allocated for a neighbor who's
address is currently tried to be resolved there was no error case
before. The packet that was tried to be put in the queue was thus not
released and stayed in the packet buffer for ever.

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