NetworkPkg: Fix Duplicate FreePool Error in WCM

NetworkPkg: Fix Duplicate FreePool Error in WCM

* REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1577

In WiFi Connection Manager scan process, the result received
from WiFi device driver will be freed twice, and will cause
unexpected errors, and even system crash.

This issue also exists in some other places potentially, this
patch is to fix these issues and also add Timer Cancelling
before Close to avoid potential NULL reference.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Wang Fan <fan.wang@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Wu Jiaxin <jiaxin.wu@intel.com>