net/mlx4_en: fix sparse warning on a cast which truncates bits from constant value

the MLX4_EN_WOL_DO_MODIFY flag which is defined through enum targets
bit 63, this triggers a "cast truncate bits from constant value
(8000000000000000 becomes 0)" warning from sparse, fix that by using
define instead of enum.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>