decoding: improve and add comments

Change-Id: I45c9fc55243224909ca2fdece8cbfa686b0f444d
Reviewed-on: https://gerrit.osmocom.org/139
Tested-by: Jenkins Builder
Reviewed-by: Harald Welte <laforge@gnumonks.org>
diff --git a/src/decoding.h b/src/decoding.h
index 1043d67..50c9e7d 100644
--- a/src/decoding.h
+++ b/src/decoding.h
@@ -28,10 +28,11 @@
 
 class Decoding {
 public:
+	/* represents (parts) LLC PDUs within one RLC Data block */
 	struct RlcData {
 		uint8_t	offset;
 		uint8_t	length;
-		bool	is_complete;
+		bool	is_complete; /* if this PDU ends in this block */
 	};
 
 	static int rlc_data_from_ul_data(