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.

Change-Id: I247fcb7c89fe23c99c580705c5f4a1d172b9c917
Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>