A DTLS type is needed for our DHT account.
This type of transport is based on UDP + TLS.
This kind of transport behaviour don't exist on
current PJSIP v2.5.5 release.
This patch adds this transport type, both for IPv4 and IPv6.
Our PJSIP bridge class is modifier to support this new type
for DHT account.
Reviewed-by: Andreas Traczyk <email@example.com>