csn1: Fix readIndex pointer change in CSN_VARIABLE_ARRAY

There's actually 3 errors:
* Its value should be updated, not the pointer itself
* Value should be increased, not decreased
* bitvec_read_field() API is already advancing it, no need to do it

Fixes: OS#4838
Change-Id: I009abc373794e148091e637ffee80c6461960945
diff --git a/tests/rlcmac/RLCMACTest.cpp b/tests/rlcmac/RLCMACTest.cpp
index f1b6508..140b2f2 100644
--- a/tests/rlcmac/RLCMACTest.cpp
+++ b/tests/rlcmac/RLCMACTest.cpp
@@ -110,6 +110,7 @@
 	"4913e00850884013a8048b2b2b2b2b2b2b2b2b2b2b2b2b", // Polling Request (malformed)
 	"412430007fffffffffffffffefd19c7ba12b2b2b2b2b2b", // Packet Uplink Ack Nack?
 	"41942b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b", // System Info 13?
+	"40883c1493120000000012002b2b2b2b2b2b2b2b2b2b2b", // Pkt Paging Request (OS#4838)
 	};
 
 	int testDataSize = sizeof(testData)/sizeof(testData[0]);