net: fix the missing unlock for detached devices

The combined condition was left as is when we converted
from __dev_get_by_index() to netdev_get_by_index_lock().
There was no need to undo anything with the former, for
the latter we need an unlock.

Fixes: 1d22d306 ("net: drop rtnl_lock for queue_mgmt operations")
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20250418015317.1954107-1-kuba@kernel.org


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