can: j1939: transport: make sure the aborted session will be deactivated only once

j1939_session_cancel() was modifying session->state without protecting
it by locks and without checking actual state of the session.

This patch moves j1939_tp_set_rxtimeout() into j1939_session_cancel()
and adds the missing locking.

Fixes: 9d71dd0c

 ("can: add support of SAE J1939 protocol")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>