net: allow out-of-order netdev unregistration

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 e6a71f2f7d4c ("vlan: move dev_put into vlan_dev_uninit")
for example.

Eric has removed the only known ordering requirement in
commit f9522a92a634 ("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>