ixgbe: fix fc autoneg ethtool reporting.

Originally ixgbe_device_supports_autoneg_fc() was only expected to
be called by copper devices.  This would lead to false information
to be displayed via ethtool.

v2: changed ixgbe_device_supports_autoneg_fc() to a bool function,
    it returns bool.  Based on feedback from David Miller

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>