Use tmate-server-port when using libssh 0.9

* Since libssh 0.9 doing ssh_connect will call parse_config
  (unless it is deactivated SSH_OPTIONS_PROCESS_CONFIG)
  if ~/.ssh/config hasn't been parsed, overwriting the port option.
  So this will call parse_first before setting the port with
  tmate-server-port as commit 89a8a6fcf07368c56a98ff8168db77b6814fbe7b.

  Fixes tmate-io#167

  Commit 89a8a6fcf07368c56a98ff8168db77b6814fbe7b in libssh

  As the configuration parsing is the last thing before doing the
  actual connection, it might overwrite previously set options.
  If this is not intended, the client application can
  ask the configuration files to be parsed before setting some other
  options that should not ve overwritten.

tmate-ssh-client.c

@@ -269,7 +269,6 @@ static void on_ssh_client_event(struct tmate_ssh_client *client)
 		ssh_set_blocking(session, 0);
 		ssh_options_set(session, SSH_OPTIONS_HOST, client->server_ip);
 		ssh_options_set(session, SSH_OPTIONS_LOG_VERBOSITY, &verbosity);
-		ssh_options_set(session, SSH_OPTIONS_PORT, &port);
 		ssh_options_set(session, SSH_OPTIONS_USER, "tmate");
 		ssh_options_set(session, SSH_OPTIONS_COMPRESSION, "yes");
 
@@ -287,6 +286,14 @@ static void on_ssh_client_event(struct tmate_ssh_client *client)
 			free(identity);
 		}
 
+		/*
+		 * libssh 0.9 calls parse_config if it hasn't been parsed
+		 * when doing a ssh_connect overwriting the port.
+		 * So this overwrites port with our tmate-server-port config.
+		 */
+		ssh_options_parse_config(session, NULL);
+		ssh_options_set(session, SSH_OPTIONS_PORT, &port);
+
 		client->state = SSH_CONNECT;
 	}
 	// fall through