Server bug fix: Allow restarts when using port= option
If the Mandos server is configured to use a specific TCP port to listen to (by using the port= option in mandos.conf or the command line --port option), that port becomes unusable for a time when the Mandos server is restarted, making restarts fail. Avoid this by, if a port number is specified, using SO_REUSEADDR when binding the listening TCP socket to a port number.
* mandos (IPv6_TCPServer.server_bind): Set self.allow_reuse_address if a port number is specified.
Reported-by: Juan Miguel Alcarria Herrera <juanmi@arco2000.es>