net: netxen: let core reject the unsupported coalescing parameters

Set ethtool_ops->supported_coalesce_params to let
the core reject unsupported coalescing parameters.

As a side effect of these changes the error code for
unsupported params changes from EINVAL to EOPNOTSUPP.

The driver was missing a check for rate_sample_interval.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>