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

Netd opens the raw socket fd and set socket option with mark.
Then, pass the prepared socket fd to clatd. This is a
preparation for reducing the clatd required capability.

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

Change-Id: Ibc46981a8a45ae048a0a707c1771888260db26c4
1 file changed