net: bridge: mcast: move querier state to the multicast context

We need to have the querier state per multicast context in order to have
per-vlan control, so remove the internal option bit and move it to the
multicast context. Also annotate the lockless reads of the new variable.

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