Start VPN as early as possible during startup

- Switch from USER_STARTING to USER_STARTED which is the foreground
  version of the broadcast

- Set the new VPN network as CONNECTING initially to avoid spamming
  apps with useless notifications ahead of the network being fully
  available

Bug: 26694104
Fix: 28335277
Change-Id: I31d5260dda62ff440c31c44eb0aa5c891e2717e5