Fix O_NONBLOCK flag loss

During syslog reconnect we lose nonblock flag. THis leads to misbehavior
while logging. Tarantool hang forever

Closes #3615

src/say.c

@@ -238,6 +238,16 @@ write_to_file(struct log *log, int total);
 static void
 write_to_syslog(struct log *log, int total);
 
+static void
+set_nonblock(int fd)
+{
+	int flags;
+	if ( (flags = fcntl(fd, F_GETFL, 0)) < 0 ||
+	     fcntl(fd, F_SETFL, flags | O_NONBLOCK) < 0) {
+		say_syserror("fcntl, fd=%i", fd);
+	}
+}
+
 /**
  * Rotate logs on SIGHUP
  */
@@ -262,13 +272,9 @@ log_rotate(struct log *log)
 	dup2(fd, log->fd);
 	close(fd);
 
-	if (log->nonblock) {
-		int flags;
-		if ( (flags = fcntl(log->fd, F_GETFL, 0)) < 0 ||
-		     fcntl(log->fd, F_SETFL, flags | O_NONBLOCK) < 0) {
-			say_syserror("fcntl, fd=%i", log->fd);
-		}
-	}
+	if (log->nonblock)
+		set_nonblock(log->fd);
+
 	/* We are in ev signal handler
 	 * so we don't have to be worry about async signal safety
 	 */
@@ -940,6 +946,8 @@ write_to_syslog(struct log *log, int total)
 			close(log->fd);
 		log->fd = log_syslog_connect(log);
 		if (log->fd >= 0) {
+			if (log->nonblock)
+				set_nonblock(log->fd);
 			/*
 			 * In a case or error the log message is
 			 * lost. We can not wait for connection -