[nrf fromtree] Bluetooth: Mesh: Fix proxy advertiser handling with GATT server enabled

When the GATT server is enabled the proxy advertiser
server need to be stopped. This solved a bug where the
Mesh Proxy Service is not restared.
This fix is done to fix several failing PTS test that
was failing when CONFIG_BT_MESH_ADV_EXT_GATT_SEPARATE
was enabled. Calling the stop_proxy_adv was left out
in a prevouis commit when doing code cleanup.

Signed-off-by: Ingar Kulbrandstad <[email protected]>
(cherry picked from commit a65a164)
Signed-off-by: Pavel Vasilyev <[email protected]>

Author: Balaklaka

subsys/bluetooth/mesh/adv_ext.c

@@ -342,12 +342,17 @@ static void start_proxy_sol_or_proxy_adv(struct bt_mesh_ext_adv *ext_adv)
 		}
 	}
 
-	if (IS_ENABLED(CONFIG_BT_MESH_GATT_SERVER) &&
-	    !atomic_test_and_set_bit(ext_adv->flags, ADV_FLAG_PROXY)) {
-		if (bt_mesh_adv_gatt_send()) {
-			atomic_clear_bit(ext_adv->flags, ADV_FLAG_PROXY);
+	if (IS_ENABLED(CONFIG_BT_MESH_GATT_SERVER)) {
+		if (stop_proxy_adv(ext_adv)) {
 			return;
 		}
+
+		if (!atomic_test_and_set_bit(ext_adv->flags, ADV_FLAG_PROXY)) {
+			if (bt_mesh_adv_gatt_send()) {
+				atomic_clear_bit(ext_adv->flags, ADV_FLAG_PROXY);
+				return;
+			}
+		}
 	}
 }