In aes_test.go, we can only test Go version of expandKey,
because AES-NI uses native endian for expanded keys, and
it's different from that of examples in FIPS 197.
As we don't expose expanded keys to the outside, i think
this is ok. And I really think if the AES-NI version get
the expanded keys wrong, it won't ever pass the other tests.
However, if you insist, i can add a traslateExpandKeys()
routine for that test.