Add rtp_test to show the double-bind bug of OS#4444

Change-Id: I6742e5504cfb827031031e4d8d49a616ab203a94
diff --git a/tests/rtp_test/rtp_test.ok b/tests/rtp_test/rtp_test.ok
new file mode 100644
index 0000000..ded2792
--- /dev/null
+++ b/tests/rtp_test/rtp_test.ok
@@ -0,0 +1,2 @@
+First bind to any random local port...
+Now try to bind another socket to the same port: FAILED - second bind to port 16384 worked