net: vxlan: lwt: Use source ip address during route lookup.

LWT user can specify destination as well as source ip address
for given tunnel endpoint. But vxlan is ignoring given source
ip address. Following patch uses both ip address to route the
tunnel packet. This consistent with other LWT implementations,
like GENEVE and GRE.

Fixes: ee122c79 ("vxlan: Flow based tunneling").
Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Acked-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>