Draft: radv: VM explicit sync.
This is an alternative take on !18032, but with the scope narrowed to VM ops (actually, just unmap ops) only.
This requires WIP kernel patches at https://github.com/ishitatsuyuki/linux/commits/explicit-sync-6.6 (applies on top of 6.6).
Like !18032, helps with stutters in Forza Horizon 5.