inet: do not use RTNL in inet_netconf_get_devconf()

"ip -4 netconf show dev XXXX" no longer acquires RTNL.

Return -ENODEV instead of -EINVAL if no netdev or idev can be found.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240227092411.2315725-3-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>