can: netlink: Add CAN_CTRLMODE_PRESUME_ACK flag

Most CAN controllers have a support for ignoring ACK absence. Some of
them refer to this feature as a self test mode (e. g. SJA1000) and some
include it as a part of a loopback mode (e. g. MCP2510).

Setting the introduced flag via netlink should make CAN controller
perform a successful transmission, even if there is no acknowledgement
(dominant ACK bit) received.

Signed-off-by: Nikita Edward Baruzdin <nebaruzdin@gmail.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>