i40e: Refactor ethtool get_settings

Previously we were only looking at the FW supported PHY types if link
was down, because we want to be more specific when link is up. This
refactor changes this. When link is down, we still rely on the FW
supported PHY types, but when link is up, we select the possible
supported link modes from what we know about the current PHY type, and
AND that with the FW supported PHY types.

Change-ID: Ice5dad83f2a17932b0b8b59f07439696ad6aa013
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>