Merge branch 'net-Export-functions-for-nexthop-code'

David Ahern says:

====================
net: Export functions for nexthop code

This set exports ipv4 and ipv6 fib functions for use by the nexthop
code. It also adds new ones to send route notifications if a nexthop
configuration changes.

v2
- repost of patches dropped at the end of the last dev window
  added patch 8 which exports nh_update_mtu since it is inline with
  the other patches
====================

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