bnxt_en: Improve ethtool .get_settings().

If autoneg is off, we should always report the speed and duplex settings
even if it is link down so the user knows the current settings.  The
unknown speed and duplex should only be used for autoneg when link is
down.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>