i386: replace hard-coded constant with appropriate macro from kernel.h

Signed-off-by: NRobert P. J. Day <rpjday@mindspring.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/asm-i386/uaccess.h

@@ -581,7 +581,7 @@ long __must_check __strncpy_from_user(char *dst,
  * If there is a limit on the length of a valid string, you may wish to
  * consider using strnlen_user() instead.
  */
-#define strlen_user(str) strnlen_user(str, ~0UL >> 1)
+#define strlen_user(str) strnlen_user(str, LONG_MAX)
 
 long strnlen_user(const char __user *str, long n);
 unsigned long __must_check clear_user(void __user *mem, unsigned long len);