gsup_client_mux_tx_error_reply(): fix: do not omit SM-RP-MR IE

The SM-RP-MR (Message Reference for SM Service) value in the response
(no matter result or error) shall match the value from the request.

Change-Id: Ifb6e749928548e6febfe7768aefe9a2a3ecf4de0
1 file changed