GSUP: fix missing osmo_gsup_get_err_msg_type()s

Add missing mappings of request to error message types in
osmo_gsup_get_error_msg_type():
* PROC_SS_REQUEST
* MO_FORWARD_SM_REQUEST
* MT_FORWARD_SM_REQUEST
* READY_FOR_SM_REQUEST

Change-Id: I801a0d6ffe09cfc75b77ab602bd25b3dc40f19c0
diff --git a/src/gsm/gsup.c b/src/gsm/gsup.c
index c1c9992..3b31d03 100644
--- a/src/gsm/gsup.c
+++ b/src/gsm/gsup.c
@@ -108,6 +108,14 @@
 		return OSMO_GSUP_MSGT_DELETE_DATA_ERROR;
 	case OSMO_GSUP_MSGT_LOCATION_CANCEL_REQUEST:
 		return OSMO_GSUP_MSGT_LOCATION_CANCEL_ERROR;
+	case OSMO_GSUP_MSGT_PROC_SS_REQUEST:
+		return OSMO_GSUP_MSGT_PROC_SS_ERROR;
+	case OSMO_GSUP_MSGT_MO_FORWARD_SM_REQUEST:
+		return OSMO_GSUP_MSGT_MO_FORWARD_SM_ERROR;
+	case OSMO_GSUP_MSGT_MT_FORWARD_SM_REQUEST:
+		return OSMO_GSUP_MSGT_MT_FORWARD_SM_ERROR;
+	case OSMO_GSUP_MSGT_READY_FOR_SM_REQUEST:
+		return OSMO_GSUP_MSGT_READY_FOR_SM_ERROR;
 	default:
 		return -1;
 	}