tracer: fix default syslog log level and doc

(cherry picked from commit 0cd20ff)

Author: razvancrainea

modules/tracer/README.md

@@ -200,7 +200,7 @@ modparam("tracer", "trace_id",
 "[tid]uri=file:/path/to/file")
 /*syslog trace id at error (level -1)*/
 modparam("tracer", "trace_id",
-"[tid]uri=syslog:local0:-1")
+"[tid]uri=syslog:LOG_LOCAL0:-1")
 ...
 ```
 
@@ -211,6 +211,9 @@ modparam("tracer", "trace_id",
 When *syslog* tracing is used, this parameter specifies
 the log facility to write traces to.
 
+Facility names must use the OpenSIPS names, such as *LOG_LOCAL0* or
+*LOG_DAEMON*. The short form *local0* is not accepted.
+
 
 *Default value is the value of *syslog_facility*.*
 

modules/tracer/tracer.c

@@ -893,9 +893,15 @@ static int mod_init(void)
 
 	if (trace_default_syslog_facility < 0)
 		trace_default_syslog_facility = log_facility;
-	if (trace_default_syslog_level != 0)
+	if (trace_default_syslog_level == 0)
 		trace_default_syslog_level = *log_level;
 
+	/* update the levels for all tids, if not explicitely set */
+	for (it = trace_list; it; it = it->next) {
+		if (it->type == TYPE_SYSLOG && it->el.syslog.level == 0)
+			it->el.syslog.level = trace_default_syslog_level;
+	}
+
 	LM_INFO("initializing...\n");
 
 	trace_on_flag = (int*)shm_malloc(sizeof(int));