lacp: Add support to recognize LACP Marker RX PDUs.

lacp: Add support to recognize LACP Marker RX PDUs.

OVS does not support the LACP Marker protocol. Typically, ToR switches
send a LACP Marker PDU when restarting LACP negotiation following a link
flap or LACP timeout.

When a LACP Marker PDU is received, OVS logs the following warning and
drops the packet:
    “lacp(pmdXXX)|WARN|bond-prv: received an unparsable LACP PDU.”

As the above message is logged around the same time the link flap or
LACP down events are logged, it gives a misleading impression that the
reception of an unparsable LACP PDU is the reason for the LACP down
event.

The proposed patch does not add support for the LACP Marker protocol.
It simply recognizes LACP Marker packets, drops them and logs a clear
message indicating that a Marker packet was a received. A counter to
track the number of such packets received is also added.

Signed-off-by: Nitin katiyar <nitin.katiyar@ericsson.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>