server: add safeguards against printing bogus port number

server: add safeguards against printing bogus port number

Clang static checker emits "Assigned value is garbage or undefined"
warning there as it can't prove that when the socket descriptor is
AF_INET/SOCK_STREAM and getsockname doesn't return an error, sin_port
is guaranteed to be filled in.

Pacify it by obvious means.

Change-Id: I43b5e5ceb41c07d523a81b34a25490c4c5f49a70
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/4350
Tested-by: jenkins
Reviewed-by: Tim Newsome <tim@sifive.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>