bnx2x: Restore FCoE 4-port devices support

bnx2x FW 1.78.17 properly supports DCBX configuration for 4-port devices,
enabling FCoE support on 57840 boards.

Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>