NetworkPkg/Ip4Dxe: Check the received package length (CVE-2019-14559).

NetworkPkg/Ip4Dxe: Check the received package length (CVE-2019-14559).

v3: correct the coding style.
v2: correct the commit message & add BZ number.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1610

This patch is to check the received package length to make sure the package
has a valid length field.

Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Siyuan Fu <siyuan.fu@intel.com>