batman-adv: Fix double-hold of meshif when getting enabled

It was originally meant to replace the dev_hold with netdev_hold. But this
was missed in batadv_hardif_enable_interface(). As result, there was an
imbalance and a hang when trying to remove the mesh-interface with
(previously) active hard-interfaces:

  unregister_netdevice: waiting for batadv0 to become free. Usage count = 3

Fixes: 00b35530 ("batman-adv: adopt netdev_hold() / netdev_put()")
Suggested-by: Eric Dumazet <edumazet@google.com>
Reported-by:  <syzbot+ff3aa851d46ab82953a3@syzkaller.appspotmail.com>
Reported-by:  <syzbot+4036165fc595a74b09b2@syzkaller.appspotmail.com>
Reported-by:  <syzbot+c35d73ce910d86c0026e@syzkaller.appspotmail.com>
Reported-by:  <syzbot+48c14f61594bdfadb086@syzkaller.appspotmail.com>
Reported-by:  <syzbot+f37372d86207b3bb2941@syzkaller.appspotmail.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250414-double_hold_fix-v5-1-10e056324cde@narfation.org


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