net: bridge: mcast: record querier port device ifindex instead of pointer

Currently when a querier port is detected its net_bridge_port pointer is
recorded, but it's used only for comparisons so it's fine to have stale
pointer, in order to dereference and use the port pointer a proper
accounting of its usage must be implemented adding unnecessary
complexity. To solve the problem we can just store the netdevice ifindex
instead of the port pointer and retrieve the bridge port. It is a best
effort and the device needs to be validated that is still part of that
bridge before use, but that is small price to pay for avoiding querier
reference counting for each port/vlan.

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