net: bridge: mcast: use br_ip's src for src groups and querier address

Now that we have src and dst in br_ip it is logical to use the src field
for the cases where we need to work with a source address such as
querier source address and group source address.

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