ORder of operations to trigger a problem:
- Start an already authed tailscaled, verify you can ping stuff.
- Run `tailscale up`. Notice you can no longer ping stuff.
The problem is that `tailscale up` stops the IPN state machine before
restarting it, which zeros out the packet filter but _not_ the packet
filter hash. Then, upon restarting IPN, the uncleared hash incorrectly
makes the code conclude that the filter doesn't need updating, and so
we stay with a zero filter (reject everything) for ever.
The fix is simply to update the filterHash correctly in all cases,
so that running -> stopped -> running correctly changes the filter
at every transition.
Signed-off-by: David Anderson <danderson@tailscale.com>
358cd3fd92