sgsn: add statistics counter for GPRS and PDP packets

Changing the test to allow still allocated block from the rate
counters.

Change-Id: Ie30e4c3084ee3a138d6b39bb5000234ac814e65f
diff --git a/openbsc/include/openbsc/gprs_sgsn.h b/openbsc/include/openbsc/gprs_sgsn.h
index 723c914..b0dd75f 100644
--- a/openbsc/include/openbsc/gprs_sgsn.h
+++ b/openbsc/include/openbsc/gprs_sgsn.h
@@ -453,4 +453,6 @@
 struct sgsn_instance;
 int sgsn_gtp_init(struct sgsn_instance *sgi);
 
+void sgsn_rate_ctr_init();
+
 #endif /* _GPRS_SGSN_H */