[RFCLAT#2] Move the packet socket creation from clatd to netd

This is a preparation for reducing the clatd required capability.

Function change:
- Opening packet socket in open_sockets() is moved to ClatdController
- remove open_sockets()

Argument change:
-r [read socket descriptor number]

Bug: 212345928
Test: manual test
1. Connect to ipv6-only wifi.
2. Try IPv4 traffic.
   $ ping 8.8.8.8

Change-Id: I912a4663dad101a4bcba30934340862572aa9318
3 files changed