It would end up resetting whatever hostinfo we had constructed
and leave the backend statemachine in a broken state.
This fixes that by storing the PushDeviceToken on the LocalBackend
and populating it on Hostinfo before passing it to controlclient.
Updates tailscale/corp#8940
Updates tailscale/corp#15367
Signed-off-by: Maisem Ali <maisem@tailscale.com>