IceTransport: make isTCPEnabled const

Change-Id: I869fcb8903654558c39afa4f9d4aaefecd7cb40a
diff --git a/include/ice_transport.h b/include/ice_transport.h
index c2d4756..a13ebdd 100644
--- a/include/ice_transport.h
+++ b/include/ice_transport.h
@@ -184,7 +184,7 @@
     bool setSlaveSession();
     bool setInitiatorSession();
 
-    bool isTCPEnabled();
+    bool isTCPEnabled() const;
 
     ICESDP parseIceCandidates(std::string_view sdp_msg);