be2net: support ethtool get-dump option

This patch adds support for ethtool's --get-dump option in be2net,
to retrieve FW dump. In the past when this option was not yet available,
this feature was supported via the --register-dump option as a workaround.
This patch removes support for FW-dump via --register-dump option as it is
now available via --get-dump option. Even though the
"ethtool --register-dump" cmd which used to work earlier, will now fail
with ENOTSUPP error, we feel it is not an issue as this is used only
for diagnostics purpose.

Signed-off-by: Venkat Duvvuru <venkatkumar.duvvuru@avagotech.com>
Signed-off-by: Sathya Perla <sathya.perla@avagotech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>