MINOR: resolvers: rework dns stats prototype because specific to resolvers

Counters are currently stored into lowlevel nameservers struct but
most of them are resolving layer data and increased in the upper layer
So this patch renames the prototype used to allocate/dump them with prefix
'resolv' waiting for a clean split.
diff --git a/src/stats.c b/src/stats.c
index 2450183..a6fe8bf 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -3580,9 +3580,9 @@
 	case STAT_ST_LIST:
 		switch (domain) {
 		case STATS_DOMAIN_DNS:
-			if (!stats_dump_dns(si, stat_l[domain],
-			                    stat_count[domain],
-			                    &stats_module_list[domain])) {
+			if (!stats_dump_resolvers(si, stat_l[domain],
+			                          stat_count[domain],
+			                          &stats_module_list[domain])) {
 				return 0;
 			}
 			break;
@@ -4691,7 +4691,7 @@
 		}
 	}
 
-	dns_stats_clear_counters(clrall, &stats_module_list[STATS_DOMAIN_DNS]);
+	resolv_stats_clear_counters(clrall, &stats_module_list[STATS_DOMAIN_DNS]);
 
 	memset(activity, 0, sizeof(activity));
 	return 1;
@@ -4940,7 +4940,7 @@
 		i += mod->stats_count;
 	}
 
-	if (!dns_allocate_counters(&stats_module_list[STATS_DOMAIN_DNS])) {
+	if (!resolv_allocate_counters(&stats_module_list[STATS_DOMAIN_DNS])) {
 		ha_alert("stats: cannot allocate all counters for dns statistics\n");
 		err_code |= ERR_ALERT | ERR_FATAL;
 		return err_code;