Provide additional lle data in IPv6 lltable dump used by ndp(8).

Before the change, things like lle state were queried via

SIOCGNBRINFO_IN6 by ndp(8) for _each_ lle entry in dump.

This ioctl was added in 1999, probably to avoid touching rtsock code.

This change maps SIOCGNBRINFO_IN6 data to standard rtsock dump the
following way:

expire (already) maps to rtm_rmx.rmx_expire
isrouter -> rtm_flags & RTF_GATEWAY
asked -> rtm_rmx.rmx_pksent
state -> rtm_rmx.rmx_state (maps to rmx_weight via define)

Reviewed by: ae