NetworkPkg/HttpDxe: Fix HTTP download OS image over 4G size failure

NetworkPkg/HttpDxe: Fix HTTP download OS image over 4G size failure

UINT32 integer overflow will happen once the download OS image over
4G size. This patch is to fix this issue.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Zhang Lubo <lubo.zhang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Sriram Subramanian <sriram-s@hpe.com>