We return a destination entry without refcount if a socket
policy is found in xfrm_lookup. This triggers a warning on
a negative refcount when freeeing this dst entry. So take
a refcount in this case to fix it.

This refcount was forgotten when xfrm changed to cache bundles
instead of policies for outgoing flows.
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>
Acked-by: NTimo Teräs <timo.teras@iki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>