Ax88772: Add logic to separate packet, fix MTU issue. Ax88772b: Fix driver model unload function, fix SCT test failures.

Signed-off-by: Yu Pei <pei.yu@intel.com>
Reviewed-by: Ouyang Qian <qian.ouyang@intel.com>
Reviewed-by: Leahy, Leroy P <Leroy.P.Leahy@intel.com>


git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14443 6f19259b-4bc3-4df7-8a09-765794883524