[CLATJ#21] ClatCoordinator: start clatd

launch clatd with the given cli arguments.

Bug: 212345928
Test: flash and boot
- run "atest ClatCoordinatorTest" in a follow commit.
- manual test
  1. Connect to ipv6-only wifi.
  2. Try IPv4 traffic.
     $ ping 8.8.8.8

Change-Id: Ie57a7c7a9d3d77396e91fa9f94c02f1ad05487c1
2 files changed