NetworkPkg: PXE Driver's LoadFile protocol should check FilePath

NetworkPkg: PXE Driver's LoadFile protocol should check FilePath

PXE driver's LoadFile protocol should check the input parameter
FilePath to see whether it's a supported device path.If not,
it should return invalid parameter, do not continue PXE boot.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Zhang Lubo <lubo.zhang@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18436 6f19259b-4bc3-4df7-8a09-765794883524