qcacld-3.0: Avoid integer underflow in dot11f_unpack functions

In function dot11f_unpack functions length of buffer passed is
decremented as pointer advances in the buffer. Add a check for
integer underflow before decrementing the length.

Change-Id: I4ed39d326855c2027ff0bc3cbe5c8981a2ae2aa1
CRs-Fixed: 2231755

core/mac/src/include/dot11f.h

@@ -1,6 +1,9 @@
 /*
  * Copyright (c) 2012-2018 The Linux Foundation. All rights reserved.
  *
+ * Previously licensed under the ISC license by Qualcomm Atheros, Inc.
+ *
+ *
  * Permission to use, copy, modify, and/or distribute this software for
  * any purpose with or without fee is hereby granted, provided that the
  * above copyright notice and this permission notice appear in all
@@ -16,6 +19,12 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
+/*
+ * This file was originally distributed by Qualcomm Atheros, Inc.
+ * under proprietary terms before Copyright ownership was assigned
+ * to the Linux Foundation.
+ */
+
 #ifndef DOT11F_H
 #define DOT11F_H
 /*
@@ -26,7 +35,7 @@
  *
  *
  * This file was automatically generated by 'framesc'
- * Wed Feb 21 17:16:54 2018 from the following file(s):
+ * Fri Apr 27 16:11:55 2018 from the following file(s):
  *
  * dot11f.frms
  *
@@ -48,6 +57,10 @@ typedef uint32_t tDOT11F_U64[2];
 #define __must_check
 #endif
 
+#if !defined unlikely
+#define unlikely(x)    (x)
+#endif
+
 /*
  * Frames Return Codes:
  *