linux/ethtool: Added macro ETH_FW_DUMP_DISABLE

o flag field of ethtool_dump structure must be initialized by this macro
value that is zero, if the firmware dump is disabled.
by this we can get the firmware dump capability [enable/disable] via ethtool

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