lacp: Don't send or receive PDUs when carrier state of slave is down

lacp: Don't send or receive PDUs when carrier state of slave is down

Fortville NICs (or their drivers) can get into an inconsistent state,
in which the NIC can actually transmit and receive packets even
though they report "PHY down". In such a state, OVS can exchange and
process LACP messages and enable a LACP slave. However, further packet
exchange over the slave fails because OVS sees that the PHY is down.

This commit fixes the problem by making OVS ignore received LACP PDUs
and suppress transmitting LACP PDUs when carrier is down. In addition,
when a LACP PDU is received with carrier down, this commit triggers
rechecking the carrier status (by incrementing the connectivity sequence
number) to ensure that it is updated as quickly as possible.

Signed-off-by: Manohar Krishnappa Chidambaraswamy <manukc@gmail.com>
Co-authored-by: Manohar Krishnappa Chidambaraswamy <manukc@gmail.com>
Signed-off-by: Nitin Katiyar <nitin.katiyar@ericsson.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>