tipc: rename udp_port in struct udp_media_addr

Context implies that port in struct "udp_media_addr" is referring
to a UDP port.

Signed-off-by: Richard Alpe <richard.alpe@ericsson.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>