LND #2740 implements a new gossiper subsystem which puts its peers into two buckets, active gossiper or passive gossiper. Active gossipers are peers communicating in the currently normal way of sharing all of their state with your node; passive gossipers are peers from which you will only request specific updates. Because most active gossipers will be sending you the same updates as all other gossipers, having more than a few of them is a waste of your bandwidth, so this code will ensure that you get a default of 3 active gossipers and then put any other gossipers into the passive category. Furthermore, the new code will try to only request updates from one active gossiper at a time in round-robin fashion to avoid syncing the same updates from different nodes. In one test described on the PR, this change reduced the amount of gossip data requested by 97.5%.