tipc: let port protocol senders use new link send function

Several functions in port.c, related to the port protocol and
connection shutdown, need to send messages. We now convert them
to use the new link send function.

Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>