ns2: Rename nsi->rate_ctr_idx to nsi->nsvc_rate_ctr_idx

We will soon get another of those indexes.

Change-Id: I68a2ef3b48097f524831dd04821824b21d6d1e18
diff --git a/src/gb/gprs_ns2_internal.h b/src/gb/gprs_ns2_internal.h
index 4a899ed..f3c68f5 100644
--- a/src/gb/gprs_ns2_internal.h
+++ b/src/gb/gprs_ns2_internal.h
@@ -128,7 +128,7 @@
 	uint16_t timeout[NS_TIMERS_COUNT];
 
 	/*! workaround for rate counter until rate counter accepts char str as index */
-	uint32_t rate_ctr_idx;
+	uint32_t nsvc_rate_ctr_idx;
 
 	/*! libmnl netlink socket for link state monitoring */
 	struct osmo_mnl *linkmon_mnl;