Use public address for outgoing responses' contact header

The public address haven't been used for responses.

Issue-Id: #4047

pjmedia/src/pjmedia/transport_loop.c

@@ -187,7 +187,6 @@ pjmedia_transport_loop_create2(pjmedia_endpt *endpt,
     if (status != PJ_SUCCESS)
         return status;
 
-    tp->base.grp_lock = grp_lock;
     pj_grp_lock_add_ref(grp_lock);
     pj_grp_lock_add_handler(grp_lock, pool, tp, &tp_loop_on_destroy);
 

pjsip/src/pjsua-lib/pjsua_acc.c

@@ -3923,7 +3923,7 @@ PJ_DEF(pj_status_t) pjsua_acc_create_uas_contact( pj_pool_t *pool,
         pjsua_init_tpselector(acc_id, &tp_sel);
     }
 
-    /* Get local address suitable to send request from */
+    /* Get local address suitable to send response from */
     pjsip_tpmgr_fla2_param_default(&tfla2_prm);
     tfla2_prm.tp_type = tp_type;
     tfla2_prm.tp_sel = &tp_sel;
@@ -3940,6 +3940,26 @@ PJ_DEF(pj_status_t) pjsua_acc_create_uas_contact( pj_pool_t *pool,
     local_addr = tfla2_prm.ret_addr;
     local_port = tfla2_prm.ret_port;
 
+    /* For UDP transport, check if we need to overwrite the address
+     * with its configured bound/public address.
+     */
+    if ((flag & PJSIP_TRANSPORT_DATAGRAM) && tfla2_prm.local_if &&
+        tfla2_prm.ret_tp)
+    {
+        int i;
+
+        for (i = 0; i < (int)PJ_ARRAY_SIZE(pjsua_var.tpdata); i++) {
+            if (tfla2_prm.ret_tp==(const void *)pjsua_var.tpdata[i].data.tp) {
+                if (pjsua_var.tpdata[i].has_cfg_addr) {
+                    pj_strdup(pool, &local_addr,
+                              &pjsua_var.tpdata[i].data.tp->local_name.host);
+                    local_port = (pj_uint16_t)
+                              pjsua_var.tpdata[i].data.tp->local_name.port;
+                }
+                break;
+            }
+        }
+    }
 
     /* Enclose IPv6 address in square brackets */
     if (tp_type & PJSIP_TRANSPORT_IPV6) {