selftests: net: bridge: update IGMP/MLD membership interval value

When I fixed IGMPv3/MLDv2 to use the bridge's multicast_membership_interval
value which is chosen by user-space instead of calculating it based on
multicast_query_interval and multicast_query_response_interval I forgot
to update the selftests relying on that behaviour. Now we have to
manually set the expected GMI value to perform the tests correctly and get
proper results (similar to IGMPv2 behaviour).

Fixes: fac3cb82 ("net: bridge: mcast: use multicast_membership_interval for IGMPv3")
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>