Compatibility issue with Zoiper and CSipSimple apps #422

1. It happens with both Zoiper and CSipSimple: they can't register UDP transports in VPN mode while TCP ones goes normal. Zoiper try to play smart and falls back to TCP transport after few minutes, so it will be better to show honest CSipSimple.
2. I don't have DNS Filtering enabled and use Google DNS in my router.
3. CSipSimple screeen attached. First two accounts there are TCP, and last one failing is UDP.
   The bug is gone swithcing to proxy mode instead of VPN.

logs: FGD-169-28205