Seek advantage of kernel readahead()

References:
1. http://man7.org/linux/man-pages/man2/posix_fadvise.2.html
2. https://www.oreilly.com/library/view/linux-system-programming/9781449341527/ch04.html

src/nnn.c

@@ -3512,6 +3512,8 @@ static int dentfill(char *path, struct entry **dents)
 			open_max = max_openfds();
 	}
 
+	posix_fadvise(fd, 0, 0, POSIX_FADV_SEQUENTIAL);
+
 	dp = readdir(dirp);
 	if (!dp)
 		goto exit;