bnx2: Use netif_carrier_off() to prevent timeout.

Based on original patch from Stanislaw Gruszka <sgruszka@redhat.com>.

Using netif_carrier_off() is better than updating all the ->trans_start
on all the tx queues.

netif_carrier_off() needs to be called after bnx2_disable_int_sync()
to guarantee no race conditions with the serdes timers that can
modify the carrier state.

If the chip or phy is reset, carrier will turn back on when we get the
link interrupt.  If there is no reset, we need to turn carrier back on
in bnx2_netif_start().  Again, the phy_lock prevents race conditions with
the serdes timers.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>