Update internal GPRS cipher API

Update internal API (for GPRS cipher implementors): make it compliant
with ETSI TS 155.22. External API left untouched.
diff --git a/TODO-RELEASE b/TODO-RELEASE
index 0939336..ffdea4b 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -1,3 +1,4 @@
-#library	what		description / commit summary line
+#library	what			description / commit summary line
+libosmogsm	internal API update	Internal API for GPRS cipher implementors updated to accommodate for arbitrary key lengths
 libosmocore	change major	external talloc dependency / internal talloc removal
 libosmocore	change major	size of ph_data_param struct changed / Extend L1SAP PH-DATA with presence information
\ No newline at end of file