net: bubble up taking netdev instance lock to callers of net_devmem_unbind_dmabuf()

A recent commit added taking the netdev instance lock
in netdev_nl_bind_rx_doit(), but didn't remove it in
net_devmem_unbind_dmabuf() which it calls from an error path.
Always expect the callers of net_devmem_unbind_dmabuf() to
hold the lock. This is consistent with net_devmem_bind_dmabuf().

(Not so) coincidentally this also protects mp_param with the instance
lock, which the rest of this series needs.

Fixes: 1d22d306 ("net: drop rtnl_lock for queue_mgmt operations")
Reviewed-by: Mina Almasry <almasrymina@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250324224537.248800-2-kuba@kernel.org


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