Clatd changes for move of libipchecksum.

libipchecksum is becoming its own library in
frameworks/libs/net and its include files are no longer under
netutils/. Adjust clatd code accordingly.

Also reorder some include files as suggested by clang-format.

Test: m
Test: atest clatd_test
Test: connects to IPv6-only wifi, testipv4.com shows 10/10
Change-Id: I5e4c73065ce828123aef7e8851227f9bdf444ff9
diff --git a/ipv6.c b/ipv6.c
index ca3e4c6..05cd3ab 100644
--- a/ipv6.c
+++ b/ipv6.c
@@ -15,12 +15,10 @@
  *
  * ipv6.c - takes ipv6 packets, finds their headers, and then calls translation functions on them
  */
+#include <arpa/inet.h>
 #include <string.h>
 
-#include <arpa/inet.h>
-
-#include "netutils/checksum.h"
-
+#include "checksum.h"
 #include "config.h"
 #include "debug.h"
 #include "dump.h"