Merge pull request #3049 from authmillenon/ng_ndp/feat/rtr-dscvry

Makefile.dep

sys/include/net/gnrc/ndp.h

sys/include/net/gnrc/ndp/internal.h

sys/include/net/gnrc/ndp/router.h

sys/net/gnrc/Makefile

sys/net/gnrc/network_layer/icmpv6/gnrc_icmpv6.c

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

sys/net/gnrc/network_layer/ipv6/netif/gnrc_ipv6_netif.c

sys/net/gnrc/network_layer/ndp/gnrc_ndp.c

sys/net/gnrc/network_layer/ndp/internal/gnrc_ndp_internal.c

sys/net/gnrc/network_layer/ndp/router/Makefile

sys/net/gnrc/network_layer/ndp/router/gnrc_ndp_router.c