Revert "tracer: always load the trace api"

This reverts commit 7791304 which forced
one to load proto_hep and define at least 1 listener for it even when HEP
was not used, in order to have the tracer module load.

modules/tracer/tracer.c

@@ -836,16 +836,23 @@ static int mod_init(void)
 
 	*trace_on_flag = trace_on;
 
-	if (trace_prot_bind(TRACE_PROTO, &tprot)) {
-		LM_ERR("Failed to bind tracing protocol!\n");
-		return -1;
-	}
-
 	/* initialize hep api */
 	for (it=trace_list;it;it=it->next) {
 		if (it->type!=TYPE_HEP)
 			continue;
 
+		if (tprot.get_trace_dest_by_name == NULL) {
+			LM_DBG("Loading tracing protocol!\n");
+			/*
+			 * if more tracing protocols shall implement the api then
+			 * this should be a modparam
+			 */
+			if (trace_prot_bind(TRACE_PROTO, &tprot)) {
+				LM_ERR("Failed to bind tracing protocol!\n");
+				return -1;
+			}
+		}
+
 		it->el.hep.hep_id = tprot.get_trace_dest_by_name(&it->el.hep.name);
 		if (it->el.hep.hep_id == NULL) {
 			LM_ERR("hep id not found!\n");