BUG/MINOR: stats: Clear a bit more counters with in cli_parse_clear_counters().

Clear MaxSslRate, SslFrontendMaxKeyRate and SslBackendMaxKeyRate when
clear counters is used, it was probably forgotten when those counters were
added.

[wt: this can probably be backported as far as 1.5 in dumpstats.c]
diff --git a/src/stats.c b/src/stats.c
index 6cbda22..25d6e65 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -3579,6 +3579,9 @@
 
 	global.cps_max = 0;
 	global.sps_max = 0;
+	global.ssl_max = 0;
+	global.ssl_fe_keys_max = 0;
+	global.ssl_be_keys_max = 0;
 	return 1;
 }