file-restore: increase RAM for ZFS and disable ARC

Even through best efforts at keeping it small, including the ZFS tools
in the initramfs seems to have exhausted the small overhead we had left
- give it a bit more RAM to compensate.

Also disable the ZFS ARC, as it's no use in such a memory constrained
environment, and we cache on the QEMU/rust layer anyway.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>

src/bin/proxmox_file_restore/qemu_helper.rs

@@ -188,11 +188,10 @@ pub async fn start_vm(
         "-initrd",
         &ramfs_path,
         "-append",
-        if debug {
-            "debug panic=1"
-        } else {
-            "quiet panic=1"
-        },
+        &format!(
+            "{} panic=1 zfs_arc_min=0 zfs_arc_max=0",
+            if debug { "debug" } else { "quiet" }
+        ),
         "-daemonize",
         "-pidfile",
         &format!("/dev/fd/{}", pid_fd.as_raw_fd()),
@@ -240,9 +239,9 @@ pub async fn start_vm(
     } else {
         // add more RAM if many drives are given
         match id {
-            f if f < 10 => 128,
-            f if f < 20 => 192,
-            _ => 256,
+            f if f < 10 => 192,
+            f if f < 20 => 256,
+            _ => 384,
         }
     };