proxmox-rrd: add option to avoid page cache for load/save

use fadvice(.., POSIX_FADV_DONTNEED) for RRD files. We read those files only once,
and always rewrite them.

Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>

src/rrd_cache.rs

@@ -53,7 +53,7 @@ fn load_callback(
     dst: DST,
 ) -> RRD {
 
-    match RRD::load(path) {
+    match RRD::load(path, true) {
         Ok(rrd) => rrd,
         Err(err) => {
             if err.kind() != std::io::ErrorKind::NotFound {