niu: Recognise original ethtool class code for AH/ESP flow hashing

When the RX network flow classification interface was originally
defined for reporting and controlling of flow hashing, AH and ESP were
not given distinct flow class codes (apparently because the Sun
Neptune hardware treats them very similarly).

For flow steering, they must be distinguished, so new and separate
flow class codes were added for AH and ESP.  But for backward-
compatibility, flow hash operations should continue to support the
original class codes.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>