headers_check fix: linux/ipv6.h

fix the following 'make headers_check' warning:

  usr/include/linux/ipv6.h:26: found __[us]{8,16,32,64} type without #include <linux/types.h>
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>

include/linux/ipv6.h

 #ifndef _IPV6_H
 #define _IPV6_H
 
+#include <linux/types.h>
 #include <linux/in6.h>
 #include <asm/byteorder.h>