vxlan: preserve type of dst_port parm for encap_bypass_if_local()

Eliminate sparse warning by maintaining type of dst_port
as __be16.

Signed-off-by: Lance Richardson <lrichard@redhat.com>
Acked-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>