net: bridge: mcast: dump ipv4 querier state

Add support for dumping global IPv4 querier state, we dump the state
only if our own querier is enabled or there has been another external
querier which has won the election. For the bridge global state we use
a new attribute IFLA_BR_MCAST_QUERIER_STATE and embed the state inside.
The structure is:
 [IFLA_BR_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

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