MdeModulePkg/Ip4Dxe: return error on memory allocate failure instead of ASSERT.

MdeModulePkg/Ip4Dxe: return error on memory allocate failure instead of ASSERT.

This patch updates the IP4 driver to use error status code instead of ASSERT
if failed to allocate memory buffer.

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