CP-34834: Don't warn on no timer value

If the calculated timer is less than the token rate then
the timeval will be all 0s and considered to be unset.
Instead of warning, detect this and set the output to
NULL so the default pselect timout can take effect.

From: Mark Syms <mark.syms@citrix.com>

Signed-off-by: Mark Syms <mark.syms@citrix.com>

diff --git a/drivers/td-rated.c b/drivers/td-rated.c
index f877b65..52dd161 100644
--- a/drivers/td-rated.c
+++ b/drivers/td-rated.c
@@ -714,9 +714,10 @@ rlb_token_settimeo(td_rlb_t *rlb, struct timeval **_tv, void *data)
 	tv->tv_sec  = us / 1000000;
 	tv->tv_usec = us % 1000000;
 
-	WARN_ON(!timerisset(tv));
-
-	*_tv = tv;
+	if (timerisset(tv))
+		*_tv = tv;
+	else
+		*_tv = NULL;
 }
 
 static void
