sgsn: add statistics counter for LLC packets

new counters are:

llc.dl_bytes
llc.ul_bytes
llc.dl_packets
llc.ul_packets

The ip payload bytes are waiting for payload compression
because those data are known then.

Change-Id: I068376d35e84283cb98523cd3097a12c55cdb709
diff --git a/openbsc/src/gprs/gprs_sgsn.c b/openbsc/src/gprs/gprs_sgsn.c
index 502ba4a..038e6f0 100644
--- a/openbsc/src/gprs/gprs_sgsn.c
+++ b/openbsc/src/gprs/gprs_sgsn.c
@@ -91,6 +91,10 @@
 };
 
 static const struct rate_ctr_desc sgsn_ctr_description[] = {
+	{ "llc.dl_bytes", "Count sent LLC bytes before giving it to the bssgp layer" },
+	{ "llc.ul_bytes", "Count sucessful received LLC bytes (encrypt & fcs correct)" },
+	{ "llc.dl_packets", "Count sucessful sent LLC packets before giving it to the bssgp layer" },
+	{ "llc.ul_packets", "Count sucessful received LLC packets (encrypt & fcs correct)" },
 	{ "gprs.attach_requested", "Received attach requests" },
 	{ "gprs.attach_accepted", "Sent attach accepts" },
 	{ "gprs.attach_rejected", "Sent attach rejects" },