[RFCLAT#1] Move the raw socket creation from clatd to netd

This is a preparation for reducing the clatd required capability.

Function change:
Opening raw socket in open_sockets() is moved to ClatdController

Argument change:
-w [write socket file descriptor number] (added)

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

Change-Id: I9b4ea3de76dffd98cbab37c4091ad1a7e688dbc2
3 files changed