cleanup - remove tun.h

Longer term we should probably just merge the clat_config
and tun_data structs, but not just yet.

Test:
  git grep '(^|[^_])tun[.]h'
  comes up empty

Bug: 144730808
Test: atest clatd_test netd_integration_test
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Original-Change: https://android-review.googlesource.com/1323171
Merged-In: I7c3a986584aa3d02519545fb928457b61247ed14
Change-Id: I7c3a986584aa3d02519545fb928457b61247ed14
diff --git a/ring.c b/ring.c
index 96a50ca..7626c6d 100644
--- a/ring.c
+++ b/ring.c
@@ -24,10 +24,10 @@
 #include <sys/mman.h>
 #include <sys/socket.h>
 
+#include "config.h"
 #include "logging.h"
 #include "ring.h"
 #include "translate.h"
-#include "tun.h"
 
 int ring_create(struct tun_data *tunnel) {
   // Will eventually be bound to htons(ETH_P_IPV6) protocol,