Make sure connection is added to m.protoConn and m.rawConn before it's Start()ed (fixes #2034)

internal/model/model_test.go

@@ -242,6 +242,9 @@ func (FakeConnection) Close() error {
 	return nil
 }
 
+func (f FakeConnection) Start() {
+}
+
 func (f FakeConnection) ID() protocol.DeviceID {
 	return f.id
 }