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/llc.cpp b/src/llc.cpp
index 88b701a..1787daa 100644
--- a/src/llc.cpp
+++ b/src/llc.cpp
@@ -60,7 +60,7 @@
 	struct msgb *msg;
 
 	while ((msg = msgb_dequeue(&queue))) {
-		bts->dropped_frame();
+		bts->llc_dropped_frame();
 		msgb_free(msg);
 	}
 }