net/mld: Fix a couple of places where I forgot to unlock the network in the previous commit.
net/mld: Implement 'Other Querier Present Timer'. This timer is used to revert to Querier mode if there is no other querier on the network. Also, fix some naming: The Done message is not just Version 1 but is used with Version 2 as well.
net/igmp: Back out some blind, backported improvements to IGMP from MLD. There are too many subtle differences in the protocols for this to be safe.