qcacmn: Add scheduler mq handler for mlme

Add mlme message queue handler as the call back for non scan commands
getting activated in the scheduler context.
Add cmd already exists enum to be returned if the command already exists
in the serialization queue.

Change-Id: I24fe453ffddbd4341459874458f11688adebc740
CRs-Fixed: 2377219

scheduler/inc/scheduler_api.h

@@ -272,6 +272,15 @@ QDF_STATUS scheduler_os_if_mq_handler(struct scheduler_msg *msg);
  */
 QDF_STATUS scheduler_timer_q_mq_handler(struct scheduler_msg *msg);
 
+/**
+ * scheduler_mlme_mq_handler() - top level message queue handler for
+ *                               mlme queue
+ * @msg: pointer to actual message being handled
+ *
+ * Return: QDF status
+ */
+QDF_STATUS scheduler_mlme_mq_handler(struct scheduler_msg *msg);
+
 /**
  * scheduler_scan_mq_handler() - top level message queue handler for
  *                               scan queue