MINOR: fd: Don't forget to reset fdtab[fd].update when a fd is added/removed

It used to be guaranteed by the polling functions on a later call but
with concurrent accesses it cannot be granted anymore.
diff --git a/include/proto/fd.h b/include/proto/fd.h
index 1efe323..38c12b6 100644
--- a/include/proto/fd.h
+++ b/include/proto/fd.h
@@ -338,6 +338,7 @@
 {
 	fdtab[fd].ev = 0;
 	fdtab[fd].new = 1;
+	fdtab[fd].updated = 0;
 	fdtab[fd].linger_risk = 0;
 	fdtab[fd].cloned = 0;
 	if (fd + 1 > maxfd)