Add SI2quater support to SI3

Advertise SI2 quater presence and location (if available) using SI3
according to 3GPP TS 44.018 ยง 10.5.2.34
diff --git a/openbsc/include/openbsc/rest_octets.h b/openbsc/include/openbsc/rest_octets.h
index 963b010..9560b14 100644
--- a/openbsc/include/openbsc/rest_octets.h
+++ b/openbsc/include/openbsc/rest_octets.h
@@ -43,7 +43,8 @@
 			 present:1;
 	} scheduling;
 	struct gsm48_si3_gprs_ind gprs_ind;
-
+	/* SI 3 specific */
+	uint8_t si2quater_indicator;
 	/* SI 4 specific */
 	struct gsm48_lsa_params lsa_params;
 	uint16_t cell_id;