Add CONFLICT all to random port test

If we're very unlucky, we can get the same port opened as an ephemeral
port by some other test.

Closes GH-17706

Author: iluuu1994

ext/standard/tests/network/bug20134.phpt

@@ -2,6 +2,8 @@
 Bug #20134 (UDP reads from invalid ports)
 --INI--
 default_socket_timeout=1
+--CONFLICTS--
+all
 --FILE--
 <?php