bts: Count the number of llc frames that were "scheduled" to be sent

This does not mean that they have been successfully transferred
to the SGSN/MS but at least that they have reached a certain point
in the message flow.
diff --git a/src/bts.cpp b/src/bts.cpp
index e4c4bfa..409b5d3 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -60,6 +60,7 @@
 	{ "sba.timedout",		"SBA Timeout          "},
 	{ "llc.timeout",		"Timedout Frames      "},
 	{ "llc.dropped",		"Dropped Frames       "},
+	{ "llc.scheduled",		"Scheduled Frames     "},
 	{ "rach.requests",		"RACH requests        "},
 };