Merge pull request #8073 from miri64/gnrc_ipv6_nib/feat/route-timeout

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

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

sys/net/gnrc/application_layer/uhcpc/gnrc_uhcpc.c

sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c

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

sys/net/gnrc/network_layer/ipv6/nib/nib.c

sys/net/gnrc/network_layer/ipv6/nib/nib_ft.c

sys/shell/commands/sc_gnrc_ipv6_nib.c

tests/gnrc_ipv6_nib/main.c

tests/gnrc_ipv6_nib_6ln/main.c

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