Merge branch 'bridgge-mcast'

Nikolay Aleksandrov says:

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net: bridge: mcast: dump querier state

This set adds the ability to dump the current multicast querier state.
This is extremely useful when debugging multicast issues, we've had
many cases of unexpected queriers causing strange behaviour and mcast
test failures. The first patch changes the querier struct to record
a port device's ifindex instead of a pointer to the port itself so we
can later retrieve it, I chose this way because it's much simpler
and doesn't require us to do querier port ref counting, it is best
effort anyway. Then patch 02 makes the querier address/port updates
consistent via a combination of multicast_lock and seqcount, so readers
can only use seqcount to get a consistent snapshot of address and port.
Patch 03 is a minor cleanup in preparation for the dump support, it
consolidates IPv4 and IPv6 querier selection paths as they share most of
the logic (except address comparisons of course). Finally the last three
patches add the new querier state dumping support, for the bridge's
global multicast context we embed the BRIDGE_QUERIER_xxx attributes
into IFLA_BR_MCAST_QUERIER_STATE and for the per-vlan global mcast
contexts we embed them into BRIDGE_VLANDB_GOPTS_MCAST_QUERIER_STATE.

The structure is:
  [IFLA_BR_MCAST_QUERIER_STATE / BRIDGE_VLANDB_GOPTS_MCAST_QUERIER_STATE]
  `[BRIDGE_QUERIER_IP_ADDRESS] - ip address of the querier
  `[BRIDGE_QUERIER_IP_PORT]    - bridge port ifindex where the querier was
                                 seen (set only if external querier)
  `[BRIDGE_QUERIER_IP_OTHER_TIMER]   -  other querier timeout
  `[BRIDGE_QUERIER_IPV6_ADDRESS] - ip address of the querier
  `[BRIDGE_QUERIER_IPV6_PORT]    - bridge port ifindex where the querier
                                   was seen (set only if external querier)
  `[BRIDGE_QUERIER_IPV6_OTHER_TIMER]   -  other querier timeout

Later we can also add IGMP version of seen queriers and last seen values
from the queries.
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