[NC#1] netd: allow netd to setup packet socket for clatd

Needed because the packet socket setup has been moved from clatd
to netd.

Test: manual test
    1. Connect to ipv6-only wifi.
    2. Try IPv4 traffic.
       $ ping 8.8.8.8
Change-Id: If6c3ba70cd7b3a44a31b8deab088303c22838da8
1 file changed