[PATCH] fix broken alpha build ptrace.c error

From: Darren Williams <dsw@gelato.unsw.edu.au>

include/asm/checksum.h:75: warning: `struct in6_addr' declared inside parameter list include/asm/checksum.h:75
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/asm-alpha/checksum.h

 #ifndef _ALPHA_CHECKSUM_H
 #define _ALPHA_CHECKSUM_H
 
+#include <linux/in6.h>
 
 /*
  *	This is a version of ip_compute_csum() optimized for IP headers,