CAN RAW sockets allow userspace to tell if a received CAN frame comes
from the same socket, another socket on the same host, or another host.
See commit 1e55659c ("can-raw: add msg_flags to distinguish local
traffic"). However, this feature is missing in CAN BCM sockets.

Add the same feature to CAN BCM sockets. When reading a received frame
(opcode RX_CHANGED) using recvmsg, two flags in msg->msg_flags may be
set following the previous convention (from CAN RAW), to distinguish
between 'own', 'local' and 'remote' CAN traffic.

Update the documentation to reflect this change.
Signed-off-by: Nicolas Maier <nicolas.maier.dev@gmail.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20240120081018.2319-1-socketcan@hartkopp.netSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>