[abis] Dispatch a IPAC restart ACK/NACK signal

* Add the NACK version to the list
* Dispatch the signal when we receive the message
* Handle it in ipaccess-config by exiting the application
diff --git a/openbsc/src/abis_nm.c b/openbsc/src/abis_nm.c
index 8a96704..bb2455d 100644
--- a/openbsc/src/abis_nm.c
+++ b/openbsc/src/abis_nm.c
@@ -1070,6 +1070,12 @@
 	case NM_MT_CONN_MDROP_LINK_ACK:
 		DEBUGP(DNM, "CONN MDROP LINK ACK\n");
 		break;
+	case NM_MT_IPACC_RESTART_ACK:
+		dispatch_signal(SS_NM, S_NM_IPACC_RESTART_ACK, NULL);
+		break;
+	case NM_MT_IPACC_RESTART_NACK:
+		dispatch_signal(SS_NM, S_NM_IPACC_RESTART_NACK, NULL);
+		break;
 	}
 
 	return 0;