[BUG] stats: session rate limit gets garbaged in the stats

The statistics page (the HTML one) displays a garbage value on frontends using
"rate-limit session" in HTTP mode.

This is due to the usage of the same buffer for the macros converting the max
session rate and the limit.

Steps to reproduce :
Configuration file example  :
listen bug :80
  mode http
  rate-limit sessions
  stats enable

Then start refreshing the statistics page.

This bug was introduced just before the release of haproxy 1.4.0.

(was commit 6cfaf9e91969c87a9eab1d58a15d2d0a3f346c9b in 1.4)
diff --git a/src/dumpstats.c b/src/dumpstats.c
index 526e0f5..f8ba702 100644
--- a/src/dumpstats.c
+++ b/src/dumpstats.c
@@ -1601,7 +1601,7 @@
 						     read_freq_ctr(&px->fe_req_per_sec),
 						     U2H0(read_freq_ctr(&px->fe_sess_per_sec)),
 						     px->counters.fe_rps_max,
-						     U2H2(px->counters.fe_sps_max),
+						     U2H1(px->counters.fe_sps_max),
 						     LIM2A2(px->fe_sps_lim, "-"));
 				} else {
 					chunk_printf(&msg,