Not link-able, since NDP and NC are missing (intentionally)

Upper layers might want to utilize the flags (e.g. to tell 6LoWPAN to elide
UDP checksums). This change allows for this by copying non-addressing related
flags to the address resolution generated netif header from the user generated
netif header.

This is a temporary quick-fix for #5122 to not have GUAs removed on an
interface.
It solves the issue by both not letting the registration run out on the router
and by not letting the lifetime of an auto-configured address expire.

This reverts commit 856e1ee0.

The existence of netif is mandatory here.

gnrc_ipv6_nc, gnrc_sixlowpan, gnrc_netdev2_eth, gnrc_ipv6, xbee, sixlowpan,
sc_gnrc_6ctx

This removes dependencies to 6LoWPAN context module if an application is built without support for it.

Also, includes a missing header.