Merge branch 'ipv6-fix-neighbour-resolution-with-raw-socket'

Nicolas Dichtel says:

====================
ipv6: fix neighbour resolution with raw socket

The first patch prepares the fix, it constify rt6_nexthop().
The detail of the bug is explained in the second patch.

v1 -> v2:
 - fix compilation warnings
 - split the initial patch
====================

Signed-off-by: David S. Miller <davem@davemloft.net>