Stasis: Add a usage note on stasis_app_get_bridge

This function returns an ast_bridge without a refcount bump and the
caller must increment the count if it intends to hold the pointer.

(closes issue ASTERISK-23588)
Review: https://reviewboard.asterisk.org/r/3450/
Reported by: Matt Jordan
........

Merged revisions 412439 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@412440 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/stasis_app.h

@@ -675,6 +675,10 @@ int stasis_app_control_remove_channel_from_bridge(
  * \since 12
  * \brief Gets the bridge currently associated with a control object.
  *
+ * \note If the bridge returned by this function is to be held for any
+ *       length of time, its refcount should be incremented until the
+ *       caller is finished with it.
+ *
  * \param control Control object for the channel to query.
  *
  * \return Associated \ref ast_bridge.