kamailio: note that NAT OPTIONS keepalive can be enabled with define WITH_NATSIPPING

etc/kamailio.cfg

@@ -41,6 +41,7 @@
 #     - install RTPProxy: http://www.rtpproxy.org
 #     - start RTPProxy:
 #        rtpproxy -l _your_public_ip_ -s udp:localhost:7722
+#     - option for NAT SIP OPTIONS keepalives: WITH_NATSIPPING
 #
 # *** To enable PSTN gateway routing execute:
 #     - define WITH_PSTN