Tidy up PortMapper::send_packet().
Tidy up PortMapper::send_packet().

This patch fixes a socket leak in send_packet(), and reworks the logic
to make it easier to follow.

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@wand.net.nz>

rsanger/RouteFlow,rsanger/RouteFlow,rsanger/RouteFlow,rsanger/RouteFlow,rsanger/RouteFlow,rsanger/RouteFlow