ethtool: strset: allow ETHTOOL_A_STRSET_COUNTS_ONLY attr

The ETHTOOL_A_STRSET_COUNTS_ONLY flag attribute was previously
not allowed to be used, but now due to the policy size reduction
we would access the tb[] array out of bounds since we tried to
check for the attribute despite it not being accepted.

Fix both issues by adding it correctly to the appropriate policy.

Fixes: ff419afa ("ethtool: trim policy tables")
Fixes: 71921690

 ("ethtool: provide string sets with STRSET_GET request")
Reported-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Tested-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>