bnx2x: resurrect RX hashing

bnx2x used to be able to set rxhash, but this was lost in the conversion
to hw_features (commit 66371c441).
Restore it and enable it by default.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
CC: Vladislav Zolotarov <vladz@broadcom.com>
CC: Eilon Greenstein <eilong@broadcom.com>
CC: Dmitry Kravkov <dmitry@broadcom.com>
CC: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>