astobj2: Avoid using temporary objects + ao2_find() with OBJ_POINTER.

There is a fairly common pattern making its way through the code base where we
put a temporary object on the stack so we can call ao2_find() with OBJ_POINTER.
The purpose is so that it can be passed into the object hash function.
However, this really seems like a hack and potentially error prone.  This patch
is a first stab at approach to avoid having to do that.

It adds a new flag, OBJ_KEY, which can be used instead of OBJ_POINTER in these
situations.  Then, the hash function can know whether it was given an object or
some custom data to hash.

The patch also changes some uses of ao2_find() for iax2_user and iax2_peer
objects to reflect how OBJ_KEY would be used.

So long, and thanks for all the fish.

Review: https://reviewboard.asterisk.org/r/1184/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@330273 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/astobj2.h

@@ -680,6 +680,16 @@ enum search_flags {
 	 * by another mechanism other that the internal ao2_lock.
 	 */
 	OBJ_NOLOCK     = (1 << 5),
+	/*!
+	 * \brief The data is hashable, but is not an object.
+	 *
+	 * This can be used when you want to be able to pass custom data
+	 * to a hash function that is not a full object, but perhaps just
+	 * a string.
+	 *
+	 * \note OBJ_KEY and OBJ_POINTER are mutually exclusive options.
+	 */
+	OBJ_KEY        = (1 << 6),
 };
 
 /*!
@@ -964,9 +974,9 @@ void *__ao2_callback_data(struct ao2_container *c, enum search_flags flags,
 
 #endif
 
-void *__ao2_find_debug(struct ao2_container *c, void *arg, enum search_flags flags, char *tag,
+void *__ao2_find_debug(struct ao2_container *c, const void *arg, enum search_flags flags, char *tag,
 		       char *file, int line, const char *funcname);
-void *__ao2_find(struct ao2_container *c, void *arg, enum search_flags flags);
+void *__ao2_find(struct ao2_container *c, const void *arg, enum search_flags flags);
 
 /*! \brief
  *