tm: cb_flags made unsigned for uac_req

(cherry picked from commit ebd1c6c75a1b832ce85d576aad134b99d47b5738)

src/modules/tm/uac.h

@@ -47,7 +47,7 @@ typedef struct uac_req
 	str *ssock;
 	str *ssockname;
 	dlg_t *dialog;
-	int cb_flags;
+	unsigned int cb_flags;
 	transaction_cb *cb;
 	void *cbp;
 	str *callid;