qed: add support for dcbx.

This patch adds the necessary driver support for Management Firmware to
configure the device/firmware with the dcbx results. Management Firmware
is responsible for communicating the DCBX and driving the negotiation,
but the driver has responsibility of receiving async notification and
configuring the results in hw/fw. This patch also adds the dcbx support for
future protocols (e.g., FCoE) as preparation to their imminent submission.

Signed-off-by: Sudarsana Reddy Kalluru <sudarsana.kalluru@qlogic.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>