Adds rate_ctr_init in the startup of osmo-pcu

Issue:Though the rate_ctr framework is used in osmo-pcu for bts statistics,
      the interval counters are always 0.
Fix:rate_ctr_init is added in the startup which arms the timer and hence
    the rate ctr intervals is displayed with proper values.

Change-Id: Ib0f33d2de9406aa7436aa9aeb6a8dabdff96383b

src/pcu_main.cpp

@@ -221,6 +221,7 @@ int main(int argc, char *argv[])
 
 	osmo_init_logging(&gprs_log_info);
 	osmo_stats_init(tall_pcu_ctx);
+	rate_ctr_init(tall_pcu_ctx);
 	gprs_ns_set_log_ss(DNS);
 	bssgp_set_log_ss(DBSSGP);