When I added IGMPv3 support I decided to follow the RFC for computing
the GMI dynamically:
" 8.4. Group Membership Interval

   The Group Membership Interval is the amount of time that must pass
   before a multicast router decides there are no more members of a
   group or a particular source on a network.

   This value MUST be ((the Robustness Variable) times (the Query
   Interval)) plus (one Query Response Interval)."

But that actually is inconsistent with how the bridge used to compute it
for IGMPv2, where it was user-configurable that has a correct default value
but it is up to user-space to maintain it. This would make it consistent
with the other timer values which are also maintained correct by the user
instead of being dynamically computed. It also changes back to the previous
user-expected GMI behaviour for IGMPv3 queries which were supported before
IGMPv3 was added. Note that to properly compute it dynamically we would
need to add support for "Robustness Variable" which is currently missing.

Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Fixes: 0436862e417e ("net: bridge: mcast: support for IGMPv3/MLDv2 ALLOW_NEW_SOURCES report")
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>