vxlan: fix byte order issues with NDA_PORT

The NDA_PORT attribute was added, but the author wasn't careful
about width (port is 16 bits), or byte order.  The attribute was
being dumped as 16 bits, but only 32 bit value would be accepted
when setting up a device. Also, the remote port is in network
byte order and was being compared with default port in host byte
order.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>