ethtool: Add direct access to ops->get_sset_count

This patch is an alternative approach for accessing string
counts, vs. the drvinfo indirect approach.  This way the drvinfo
space doesn't run out, and we don't break ABI later.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>