MT#59962 _trans_layer: `update_uac_request()` use ref. to ptr

To be able to set msg's ptr to NULL in the `update_uac_request()`
after the memory referenced via it is freed.

Change-Id: Id8d89a6a64b78e5fd06d43e0b99aaf83c4623908

core/sip/trans_layer.cpp

@@ -2065,7 +2065,7 @@ int _trans_layer::update_uac_reply(trans_bucket* bucket, sip_trans* t, sip_msg*
 }
 
 int _trans_layer::update_uac_request(trans_bucket* bucket, sip_trans*& t,
-				     sip_msg* msg)
+				     sip_msg*& msg)
 {
     if(msg->u.request->method != sip_request::ACK){
 	t = bucket->add_trans(msg,TT_UAC);

core/sip/trans_layer.h

@@ -278,7 +278,7 @@ protected:
      * @return transaction state if successfull
      */
     int update_uac_reply(trans_bucket* bucket, sip_trans* t, sip_msg* msg);
-    int update_uac_request(trans_bucket* bucket, sip_trans*& t, sip_msg* msg);
+    int update_uac_request(trans_bucket* bucket, sip_trans*& t, sip_msg*& msg);
 
     /**
      * Implements the state changes for the UAS state machine