Merge branch 'udp-tunnel-route-lookups'

Beniamino Galvani says:

====================
net: consolidate IPv4 route lookup for UDP tunnels

At the moment different UDP tunnels rely on different functions for
IPv4 route lookup, and those functions all implement the same
logic. Only bareudp uses the generic ip_route_output_tunnel(), while
geneve and vxlan basically duplicate it slightly differently.

This series first extends the generic lookup function so that it is
suitable for all UDP tunnel implementations. Then, bareudp, geneve and
vxlan are adapted to use them.

This results in code with less duplication and hopefully better
maintainability.

After this series is merged, IPv6 will be converted in a similar way.

Changelog:
v2
 - fix compilation with IPv6 disabled
====================

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