bnx2x: Add support for single-port DCBx

Driver is currently looking at shared information for determining whether
DCBx can be supported for a given port.
On 4-port devices, up-to-date management firmware can support DCBx on
each port of a given engine independently - but that would cause bnx2x to
misinterpert the support and assume DCBx is supported on both.

Signed-off-by: Yuval Mintz <Yuval.Mintz@qlogic.com>
Signed-off-by: Ariel Elior <Ariel.Elior@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>