qcacld-3.0: Change the underlying type of hdd_handle_t

Currently hdd_handle_t is defined as a void pointer. This is
convenient from an information hiding point of view since that means a
non-HDD component cannot dereference an HDD handle to access HDD
private data. However this is not convenient from a defect prevention
point of view since the C standard allows any other pointer type to be
freely and silently converted to and from a void pointer, and hence
the compiler is unable to detect when an HDD handle is used in a
context where a different pointer type is expected.

An example of one such defect was addressed by Change-Id
I2bbf1bf4a7975e5cb44066b6a3b1a98e82df9fad (qcacld-3.0: Fix bad param
passed during QoS Map conversion).

To help prevent this kind of defect change the definition of
hdd_handle_t to be a pointer to an opaque struct.

Change-Id: I6e885f84c0554bbe5c8582474fddb65ab6a0fdac
CRs-Fixed: 2254907

core/mac/inc/sir_types.h

@@ -51,7 +51,13 @@ typedef void *tHalHandle;
  * The HDD must be able to derive it's internal instance structure
  * pointer through this handle.
  */
-typedef void *hdd_handle_t;
+/*
+ * NOTE WELL: struct opaque_hdd_handle is not defined anywhere. This
+ * reference is used to help ensure that a hdd_handle_t is never used
+ * where a different handle type is expected
+ */
+struct opaque_hdd_handle;
+typedef struct opaque_hdd_handle *hdd_handle_t;
 
 /* ********************************************** *
 *                                                *