openvswitch: fix struct geneve_port member name

commit 6b001e68

 ("openvswitch: Use Geneve device.")

The commit above introduced 'port_no' as the name for the member of
struct geneve_port. The correct name should be 'dst_port' as described
in the kernel doc. Let's fix that member name and all the pertinent
instances so that both doc and code would be consistent.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>