OS2BMC feature will allow the server to communicate with the on-board
BMC/idrac (Baseboard Management Controller) over the LOM via
standard Ethernet.

When OS2BMC feature is enabled, the LOM will filter traffic coming
from the host. If the destination MAC address matches the iDRAC MAC
address, it will forward the packet to the NC-SI side band interface
for iDRAC processing. Otherwise, it would send it out on the wire to
the external network. Broadcast and multicast packets are sent on the
side-band NC-SI channel and on the wire as well. Some of the packet
filters are not supported in the NIC and hence driver will identify
such packets and will hint the NIC to send those packets to the BMC.
This is done by duplicating packets on the management ring. Packets
are sent to the management ring, by setting mgmt bit in the wrb header.
The NIC will forward the packets on the management ring to the BMC
through the side-band NC-SI channel.

Please refer to this online document for more details,
http://www.dell.com/downloads/global/products/pedge/
os_to_bmc_passthrough_a_new_chapter_in_system_management.pdf
Signed-off-by: Venkat Duvvuru <VenkatKumar.Duvvuru@Emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>