can: flexcan: export flexcan_ethtool_ops and remove flexcan_set_ethtool_ops()

The function flexcan_set_ethtool_ops() does one thing: populate
net_device::ethtool_ops. Instead, it is possible to directly assign
this field and remove one function call and slightly reduce the object
size. To do so, export flexcan_ethtool_ops so it becomes visible to
flexcan-core.c.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/all/20220727104939.279022-4-mailhol.vincent@wanadoo.fr


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>