MdeModulePkg UefiPxeBcDxe: Fix build error for lastest VS2015 compiler

MdeModulePkg UefiPxeBcDxe: Fix build error for lastest VS2015 compiler

The UefiPxeBcDxe module encounters a build error for IA32 arch using the
latest version of VS2015:

UefiPxe4BcDxe.lib(PxeBcDhcp.obj) : error LNK2001: unresolved external
symbol __allmul

The cause is line 1659 in file
MdeModulePkg/Universal/Network/UefiPxeBcDxe/PxeBcDhcp.c. The third
parameter for gBS->SetTimer() function is of type UINT64, so the
multiplication should use the MultU64x32() function.

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 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-By: Wu Jiaxin <jiaxin.wu@intel.com>