qcacld-3.0: Add flush callback for umac stop

During the scheduler_stop it tries to flush all the pending messages
in the queue, during the same the flush callbacks of all the pending
messages are invoked. If there is no flush callback for
SYS_MSG_ID_UMAC_STOP, it will free the bodyptr of the message which
contains the global variable g_stop_evt, which can result in invalid
access in the other thread.

Add a dummy flush callback message for the sys_stop message to
avoid the invalid access.

Change-Id: I46ca4240d787dce5b21cc2f99ced66a4c01b737c
CRs-Fixed: 2537773
1 file changed