Convert uid hash to hlist

Surprisingly, but (spotted by Alexey Dobriyan) the uid hash still uses
list_heads, thus occupying twice as much place as it could.  Convert it to
hlist_heads.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 1101b0c..b5f41d4 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -11,7 +11,7 @@
 
 struct user_namespace {
 	struct kref		kref;
-	struct list_head	uidhash_table[UIDHASH_SZ];
+	struct hlist_head	uidhash_table[UIDHASH_SZ];
 	struct user_struct	*root_user;
 };