[BUG] proxy: connection rate limiting was eating lots of CPU

The rate-limit feature relied on a timer to define how long a frontend
must remain idle. It was not considering the pending connections, so it
was almost always ready to be used again and only the accept's limit was
preventing new connections from coming in. By accounting for the pending
connection, we can compute a correct delay and effectively make the
frontend go idle for that (short) time.
diff --git a/src/proxy.c b/src/proxy.c
index 1ee4d6d..7971a7c 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -485,7 +485,7 @@
 				goto do_block;
 
 			if (p->fe_sps_lim &&
-			    (wait = next_event_delay(&p->fe_sess_per_sec, p->fe_sps_lim, 0))) {
+			    (wait = next_event_delay(&p->fe_sess_per_sec, p->fe_sps_lim, 1))) {
 				/* we're blocking because a limit was reached on the number of
 				 * requests/s on the frontend. We want to re-check ASAP, which
 				 * means in 1 ms before estimated expiration date, because the