net: ipv6: Use the nexthop when sending the packet

We must use the nexthop instead of destination address
when sending the packet. The current code mixed destination
and nexthop addresses and ignored the nexthop when sending
neighbor solicitation message.

Change-Id: I53887c16ef6fcf8365f1f47ab5792cb208dd273e
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>