There's no reason why loopback and listen only should not be allowed
at the same time. Replace the "else if" by "if" to reflect this in the
code.

Link: https://lore.kernel.org/all/20221019221016.1659260-2-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>