net: allow out-of-order netdev unregistration

Sprinkle for each loops to allow netdevices to be unregistered
out of order, as their refs are released.

This prevents problems caused by dependencies between netdevs
which want to release references in their ->priv_destructor.
See commit d6ff94af ("vlan: move dev_put into vlan_dev_uninit")
for example.

Eric has removed the only known ordering requirement in
commit c002496b

 ("Merge branch 'ipv6-loopback'")
so let's try this and see if anything explodes...

Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/r/20220215225310.3679266-2-kuba@kernel.org


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