bnxt_en: Improve link up detection.

In bnxt_update_phy_setting(), ethtool_get_link_ksettings() and
bnxt_disable_an_for_lpbk(), we inconsistently use netif_carrier_ok()
to determine link.  Instead, we should use bp->link_info.link_up
which has the true link state.  The netif_carrier state may be off
during self-test and while the device is being reset and may not always
reflect the true link state.

By always using bp->link_info.link_up, the code is now more
consistent and more correct.  Some unnecessary link toggles are
now prevented with this patch.

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