gsup: Extract the QoS field

Add roundtrip test for the new QoS IE. It will be consumed in
later commits.
diff --git a/openbsc/src/gprs/gprs_gsup_messages.c b/openbsc/src/gprs/gprs_gsup_messages.c
index 56f78fd..cb14fa1 100644
--- a/openbsc/src/gprs/gprs_gsup_messages.c
+++ b/openbsc/src/gprs/gprs_gsup_messages.c
@@ -94,6 +94,11 @@
 			pdp_info->apn_enc_len = value_len;
 			break;
 
+		case GPRS_GSUP_PDP_QOS_IE:
+			pdp_info->qos_enc = value;
+			pdp_info->qos_enc_len = value_len;
+			break;
+
 		default:
 			LOGP(DGPRS, LOGL_ERROR,
 			     "GSUP IE type %d not expected in PDP info\n", iei);
@@ -333,6 +338,11 @@
 			     pdp_info->apn_enc_len, pdp_info->apn_enc);
 	}
 
+	if (pdp_info->qos_enc) {
+		msgb_tlv_put(msg, GPRS_GSUP_PDP_QOS_IE,
+				pdp_info->qos_enc_len, pdp_info->qos_enc);
+	}
+
 	/* Update length field */
 	*len_field = msgb_length(msg) - old_len;
 }