Ensure header files using __BEGIN_DECLS include sys/cdefs.h.

We keep fixing these one-by-one; let's fix them all at once.

Found thus:

  find . -name *.h | xargs grep -L sys/cdefs.h | xargs grep -l BEGIN_DECL | xargs grep -L sys/types

Change-Id: I188842aa2484dc6176e96556d57c38a0f785b59b

libc/include/netinet/in.h

@@ -29,11 +29,13 @@
 #define _NETINET_IN_H_
 
 #include <endian.h>
+#include <netinet/in6.h>
+#include <sys/cdefs.h>
 #include <sys/socket.h>
+
 #include <linux/in.h>
 #include <linux/in6.h>
 #include <linux/ipv6.h>
-#include <netinet/in6.h>
 
 __BEGIN_DECLS