Compacting on startup means nodes may compact at a different cadence
based on whether they're long-running or restarting frequently.
We already compact after every sync, which only occurs when the TKA
state has changed. Waiting for TKA changes to trigger compaction on
nodes means compaction will occur more consistently across a tailnet.
Updates tailscale/corp#33537
Change-Id: Ia0aa6d9e5e362e9ab08450fde69772841790d5b5
Signed-off-by: Alex Chan <alexc@tailscale.com>