net: enetc: allow the enetc_reconfigure() callback to fail

enetc_reconfigure() was modified in commit c33bfaf9

 ("net: enetc:
set up XDP program under enetc_reconfigure()") to take an optional
callback that runs while the netdev is down, but this callback currently
cannot fail.

Code up the error handling so that the interface is restarted with the
old resources if the callback fails.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>