[JFFS2][XATTR] '#include <linux/list.h>' was added into xattr.h.

'#include <linux/list.h>' was added into xattr.h.
because 'struct list_head' is used in this header file.

[6/10] jffs2-xattr-v5.1-06-add_list.h.patch

Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>