Drivers might have error messages to propagate to user space, most
common being that they support a single mirror port.

Propagate the netlink extack so that they can inform user space in a
verbal way of their limitations.
Signed-off-by: NVladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>