bridge: vlan: use rcu list for the ordered vlan list

When I did the conversion to rhashtable I missed the required locking of
one important user of the vlan list - br_get_link_af_size_filtered()
which is called:
br_ifinfo_notify() -> br_nlmsg_size() -> br_get_link_af_size_filtered()
and the notifications can be sent without holding rtnl. Before this
conversion the function relied on using rcu and since we already use rcu to
destroy the vlans, we can simply migrate the list to use the rcu helpers.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>