vxlan: Fix sparse warnings

This patch fixes sparse warnings when incorrectly handling the port number
and using int instead of unsigned int iterating through &vn->sock_list[].
Keeping the port as __be16 also makes things clearer wrt endianess.
Also, it was pointed out that vxlan_get_rx_port() had unnecessary checks
which got removed.

Signed-off-by: Joseph Gasparakis <joseph.gasparakis@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>