MdeModulePkg/UefiPxeBcDxe: Fix the PXE BootMenu selection issue

MdeModulePkg/UefiPxeBcDxe: Fix the PXE BootMenu selection issue

Currently implementation doesn't accept the input during the user
is trying to select the PXE BootMenu from option 43. This path is
to fix that problem.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>