MdeModulePkg/UefiPxeBcDxe: Discard the normal ICMP packets and recycle the received...

MdeModulePkg/UefiPxeBcDxe: Discard the normal ICMP packets and recycle the received ICMP data.

This patch is to discard the normal ICMP packets and recycle the received
ICMP data to avoid the memory leak.

Cc: Siyuan Fu <siyuan.fu@intel.com>
Cc: Heyi Guo <heyi.guo@linaro.org>
Cc: Ye Ting <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Tested-by: Heyi Guo <heyi.guo@linaro.org>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>