Merge branch 'unified-tunnel-dst-caching'

Paolo Abeni says:

====================
net: unify dst caching for tunnel devices

This patch series try to unify the dst cache implementations currently
present in the kernel, namely in ip_tunnel.c and ip6_tunnel.c, introducing a
new generic implementation, replacing the existing ones, and then using
the new implementation in other tunnel devices which currently lack it.

The new dst implementation is compiled, as built-in, only if any device using
it is enabled.

Caching the dst for the tunnel remote address gives small, but measurable,
performance improvement when tunneling over ipv4 (in the 2%-4% range) and
significant ones when tunneling over ipv6 (roughly 60% when no
fragmentation/segmentation take place and the tunnel local address
is not specified).

v2:
- move the vxlan dst_cache usage inside the device lookup functions
- fix usage after free for lwt tunnel moving the dst cache storage inside
  the dst_metadata,
- sparse codying style cleanup
====================

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