can: j1939: Extend stack documentation with buffer size behavior

can: j1939: Extend stack documentation with buffer size behavior

Extend the J1939 stack documentation to include information about how
buffer sizes influence stack behavior, detailing handling of simple
sessions, TP, and ETP transfers.

Additionally, describe various setsockopt(2) options, including their
usage  and potential error values that can be returned by the stack.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20241013181715.3488980-1-o.rempel@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>