Use a raw socket to send IPv6 packets instead of a tun.

This will allow us to bind the socket to a particular network.

(cherry picked from commit 10e8827d636a72a7bcdfd52d15bad9342ae2a0a6)

Bug: 15340961
Change-Id: I0b62ef96364a90b9c0a9e3ac3ba97b5c19c89b69
diff --git a/clatd.h b/clatd.h
index 29c9ace..0a48013 100644
--- a/clatd.h
+++ b/clatd.h
@@ -33,7 +33,7 @@
 
 struct tun_data {
   char device6[IFNAMSIZ], device4[IFNAMSIZ];
-  int fd6, fd4;
+  int read_fd6, write_fd6, fd4;
 };
 
 #endif /* __CLATD_H__ */