ixgbe: Manual AN-37 for troublesome link partners for X550 SFI

Some (Juniper MX5) SFP link partners exhibit a disinclination to
autonegotiate with X550 configured in SFI mode.  This patch enables
a manual AN-37 restart to work around the problem.

Signed-off-by: Jeff Daly <jeffd@silicom-usa.com>
Tested-by: Dave Switzer <david.switzer@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>