kamailio.cfg: handle retransmissions also for request within dialog

- skip ACK, it is not a standard transaction by itself

(cherry picked from commit 868f9996f39dd76707ed09fce980893bab7c31bc)

etc/kamailio.cfg

@@ -470,18 +470,20 @@ request_route {
 		exit;
 	}
 
+	# handle retransmissions
+	if (!is_method("ACK")) {
+		if(t_precheck_trans()) {
+			t_check_trans();
+			exit;
+		}
+		t_check_trans();
+	}
+
 	# handle requests within SIP dialogs
 	route(WITHINDLG);
 
 	### only initial requests (no To tag)
 
-	# handle retransmissions
-	if(t_precheck_trans()) {
-		t_check_trans();
-		exit;
-	}
-	t_check_trans();
-
 	# authentication
 	route(AUTH);