[skip ci] Avoid potential network port conflict in tests

These tests:

- ext/standard/tests/network/udp4loop.phpt
- ext/sockets/tests/socket_create_listen.phpt
- ext/sockets/tests/socket_create_listen-win32.phpt

all use port 31338. socket_create_listen.phpt and its win32 variant are mutually
exclusive, so they can't conflict. While udp4loop.phpt tries multiple ports, the
other tests do not. If udp4loop.phpt runs first and socket_create_listen.phpt
starts before it ends, the port is still blocked. Bump the start port for
udp4loop.phpt to avoid conflicts.

Author: iluuu1994

ext/standard/tests/network/udp4loop.phpt

@@ -3,7 +3,7 @@ Streams Based IPv4 UDP Loopback test
 --FILE--
 <?php
     /* Setup socket server */
-    for ($port = 31338; $port < 31500; ++$port) {
+    for ($port = 31339; $port < 31500; ++$port) {
       $uri = "udp://127.0.0.1:$port";
       $server = @stream_socket_server($uri, $errno, $errstr, STREAM_SERVER_BIND);
       if ($server) break;