support for gateways sending TLS with SRTP but not dtls (#66)

lib/utils.js

@@ -41,6 +41,9 @@ function makeRtpEngineOpts(req, srcIsUsingSrtp, dstIsUsingSrtp, teams = false) {
   };
 }
 
+const SdpDoesNotWantDTLS = (sdp) => {
+  return /m=audio.*\s+RTP\/SAVP/.test(sdp);
+};
 const SdpWantsSrtp = (sdp) => {
   return /m=audio.*SAVP/.test(sdp);
 };
@@ -178,6 +181,7 @@ const parseConnectionIp = (sdp) => {
 module.exports = {
   isWSS,
   SdpWantsSrtp,
+  SdpDoesNotWantDTLS,
   getAppserver,
   makeRtpEngineOpts,
   makeAccountCallCountKey,