Bug 1461904: Make sure to call disconnect_all on STS. r=drno

MozReview-Commit-ID: 2WZxajc4FZz

--HG--
extra : rebase_source : 042476cea953c8abeaba9b208dfbba0ab84c8b2e

media/mtransport/test/transport_unittests.cpp

@@ -476,6 +476,7 @@ class TransportTestPeer : public sigslot::has_slots<> {
 
 
   void DestroyFlow() {
+    disconnect_all();
     if (flow_) {
       loopback_->Disconnect();
       flow_ = nullptr;