MEDIUM: counters: use sc0/sc1/sc2 instead of sc1/sc2/sc3

It was a bit inconsistent to have gpc start at 0 and sc start at 1,
so make sc start at zero like gpc. No previous release was issued
with sc3 anyway, so no existing setup should be affected.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index d74dfe0..b3435ef 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -6367,7 +6367,7 @@
 		list_for_each_entry(trule, &curproxy->tcp_req.l4_rules, list) {
 			struct proxy *target;
 
-			if (trule->action < TCP_ACT_TRK_SC1 || trule->action > TCP_ACT_TRK_SC3)
+			if (trule->action < TCP_ACT_TRK_SC0 || trule->action > TCP_ACT_TRK_SC2)
 				continue;
 
 			if (trule->act_prm.trk_ctr.table.n)
@@ -6406,7 +6406,7 @@
 		list_for_each_entry(trule, &curproxy->tcp_req.inspect_rules, list) {
 			struct proxy *target;
 
-			if (trule->action < TCP_ACT_TRK_SC1 || trule->action > TCP_ACT_TRK_SC3)
+			if (trule->action < TCP_ACT_TRK_SC0 || trule->action > TCP_ACT_TRK_SC2)
 				continue;
 
 			if (trule->act_prm.trk_ctr.table.n)