can: dev: can_get_ctrlmode_str: use capitalized ctrlmode strings

can: dev: can_get_ctrlmode_str: use capitalized ctrlmode strings

Unify the ctrlmode related strings to the command line options of the
'ip' tool from the iproute2 package. The capitalized strings are also
shown when the detailed interface configuration is printed by 'ip'.

Suggested-by: Stephane Grosjean <stephane.grosjean@hms-networks.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20251126-canxl-v8-1-e7e3eb74f889@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>