add da for fbsd 5

src/lib9/_p9dir.c

diff --git a/src/lib9/_p9dir.c b/src/lib9/_p9dir.c
index 2028c1a..57f4648 100644
--- a/src/lib9/_p9dir.c
+++ b/src/lib9/_p9dir.c
@@ -26,6 +26,7 @@
 	43,	/* vn */
 	3,	/* wd */
 	87,	/* wfd */
+	4,	/* da on FreeBSD 5 */
 };
 static int
 isdisk(struct stat *st)