Disable zram on minimal netvm/usbvm

Those run with minimal amount of memory, and there is no place to spare
some for compressed swap. Real swap is slower, but it's still better
than killing processes on OOM...

QubesOS/qubes-issues#10703

Author: marmarek

vm-systemd/setup-minimal-vm

@@ -33,7 +33,20 @@ setup_minimal_netvm() {
 	fi
 }
 
+disable_zram() {
+    systemctl mask --runtime --now systemd-zram-setup@zram0
+    ln -nsf /dev/null /run/systemd/zram-generator.conf
+    systemctl daemon-reload
+    if command -v zramctl >/dev/null; then
+        zramctl -r zram0
+    fi
+}
+
 if is_minimal_netvm; then
 	setup_minimal_netvm
+    disable_zram
 fi
 
+if is_minimal_usbvm; then
+    disable_zram
+fi