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