bnx2x: Disable local BHes to prevent a dead-lock situation

According to Eric's suggestion:
Disable local BHes to prevent a dead-lock situation between sch_direct_xmit()
(Soft_IRQ context) and bnx2x_tx_int (called by bnx2x_run_loopback() - syscall
context), as both are taking a netif_tx_lock().

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Vladislav Zolotarov <vladz@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>