Fix GPRS PUAN encoding: wrong BSN status

Earlier there was an incorrect encoding of BSN status in GPRS PUAN message.
This was a bottle neck for GPRS performance testing for UL. Which has been fixed
in this patch.

Related: OS#1806

Change-Id: I98e586aa5cb9200cf03e092556304211d4d459aa
diff --git a/src/rlc.cpp b/src/rlc.cpp
index e69d1fc..ee2635a 100644
--- a/src/rlc.cpp
+++ b/src/rlc.cpp
@@ -227,7 +227,7 @@
 {
 	int i;
 	for (i=0; i < ws(); i++) {
-		if (m_v_n.is_received(ssn()-1-i))
+		if (m_v_n.is_received((ssn()-1-i) & mod_sns()))
 			rbb[ws()-1-i] = 'R';
 		else
 			rbb[ws()-1-i] = 'I';