chainntnfs/neutrinonotify: make filter update synchronous
chainntnfs/neutrinonotify: make filter update synchronous

In this commit, we modify the notifier to handle filter updates
synchronously. We do this to prevent race conditions between new block
notifications and filter updates. Otherwise, it's possible for a new
block to come in that should match our filter, but doesn't due to the
filter being updated after.

We also modify their order so that the filter is updated first. We do
this so we can immediately start watching for the event at tip while the
rescan is ongoing.

LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd,LightningNetwork/lnd