bnx2x: avoid TX timeout when stopping device

When stop device call netif_carrier_off() just after disabling TX queue to
avoid possibility of netdev watchdog warning and ->ndo_tx_timeout() invocation.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>