headers_check fix: linux/icmpv6.h

fix the following 'make headers_check' warning:

  usr/include/linux/icmpv6.h:8: found __[us]{8,16,32,64} type without #include <linux/types.h>
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>

include/linux/icmpv6.h

 #ifndef _LINUX_ICMPV6_H
 #define _LINUX_ICMPV6_H
 
+#include <linux/types.h>
 #include <asm/byteorder.h>
 
 struct icmp6hdr {