llc: Keep track of the number of stored LLC octets

To get the number of LLC octets that are stored in the queue, this
commit adds a m_queue_octets member along with a octets() method.
This value is updated similarly to m_queue_size on each modifying
method call.

Sponsored-by: On-Waves ehf
diff --git a/src/llc.cpp b/src/llc.cpp
index d847c87..3388db1 100644
--- a/src/llc.cpp
+++ b/src/llc.cpp
@@ -100,12 +100,14 @@
 {
 	INIT_LLIST_HEAD(&m_queue);
 	m_queue_size = 0;
+	m_queue_octets = 0;
 	m_avg_queue_delay = 0;
 }
 
 void gprs_llc_queue::enqueue(struct msgb *llc_msg)
 {
 	m_queue_size += 1;
+	m_queue_octets += msgb_length(llc_msg) - 2*sizeof(struct timeval);
 	msgb_enqueue(&m_queue, llc_msg);
 }
 
@@ -120,6 +122,7 @@
 	}
 
 	m_queue_size = 0;
+	m_queue_octets = 0;
 }
 
 #define ALPHA 0.5f
@@ -136,6 +139,7 @@
 		return NULL;
 
 	m_queue_size -= 1;
+	m_queue_octets -= msgb_length(msg) - 2*sizeof(struct timeval);
 
 	/* take the second time */
 	gettimeofday(&tv_now, NULL);