abis_nm: Introduce new signal S_NM_GET_ATTR_REP

This signal can be used for tools willing to request and parse Attribute Response
and do something with the information. ipaccess-config tool will use
this signal in later patch Change-Id Ida416a969a3309868d6f4e50f34b34f224c32dd6.

Related: OS#3624
Change-Id: I9a121bbfe1b96904d4e16845abc90bb6ef20d2c9
diff --git a/include/osmocom/bsc/signal.h b/include/osmocom/bsc/signal.h
index 1b351aa..62a3d2c 100644
--- a/include/osmocom/bsc/signal.h
+++ b/include/osmocom/bsc/signal.h
@@ -72,6 +72,7 @@
 	S_NM_STATECHG_ADM,	/* Administrative State changed */
 	S_NM_OM2K_CONF_RES,	/* OM2K Configuration Result */
 	S_NM_OPSTART_ACK,	/* Received OPSTART ACK, arg is struct msgb *oml_msg */
+	S_NM_GET_ATTR_REP,	/* Received Get Attributes Response, arg is struct msgb *oml_msg */
 };
 
 /* SS_LCHAN signals */