Merge pull request #6325 from miri64/gnrc_ipv6_nib/feat/internal

Makefile.dep

sys/include/net/gnrc/ipv6/nib.h

sys/include/net/gnrc/ipv6/nib/conf.h

sys/include/net/gnrc/ipv6/nib/nc.h

sys/net/gnrc/Makefile

sys/net/gnrc/network_layer/ipv6/nib/Makefile

sys/net/gnrc/network_layer/ipv6/nib/_nib-internal.c

sys/net/gnrc/network_layer/ipv6/nib/_nib-internal.h

tests/unittests/tests-gnrc_ipv6_nib/Makefile

tests/unittests/tests-gnrc_ipv6_nib/Makefile.include

...ttests/tests-gnrc_ipv6_nib/tests-gnrc_ipv6_nib-internal.c

tests/unittests/tests-gnrc_ipv6_nib/tests-gnrc_ipv6_nib.c

tests/unittests/tests-gnrc_ipv6_nib/tests-gnrc_ipv6_nib.h