fou: always use be16 for port

udp_config.local_udp_port is be16. And iproute2 passes
network order for FOU_ATTR_PORT.

This doesn't fix any bug, just for consistency.

Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>