MEDIUM: log: add a log level override value in struct session

This log level will be used in a further patch to change the log level
depending on the request or response.
diff --git a/src/log.c b/src/log.c
index 627351f..8f8fd8f 100644
--- a/src/log.c
+++ b/src/log.c
@@ -1528,9 +1528,18 @@
 	if (LIST_ISEMPTY(&s->fe->logsrvs))
 		return;
 
-	level = LOG_INFO;
-	if (err && (s->fe->options2 & PR_O2_LOGERRORS))
-		level = LOG_ERR;
+	if (s->logs.level) { /* loglevel was overridden */
+		if (s->logs.level == -1) {
+			s->logs.logwait = 0; /* logs disabled */
+			return;
+		}
+		level = s->logs.level - 1;
+	}
+	else {
+		level = LOG_INFO;
+		if (err && (s->fe->options2 & PR_O2_LOGERRORS))
+			level = LOG_ERR;
+	}
 
 	tmplog = update_log_hdr();
 	size = tmplog - logline;