tipc: accept PACKET_MULTICAST packets

tipc: accept PACKET_MULTICAST packets

On L2 bearers, the TIPC broadcast function is sending out packets using
the corresponding L2 broadcast address. At reception, we filter such
packets under the assumption that they will also be delivered as
broadcast packets.

This assumption doesn't always hold true. Under high load, we have seen
that a switch may convert the destination address and deliver the packet
as a PACKET_MULTICAST, something leading to inadvertently dropped
packets and a stale and reset broadcast link.

We fix this by extending the reception filtering to accept packets of
type PACKET_MULTICAST.

Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>