segfault on loadvm after migrate_set_capability multifd on
Description of problem:
A segfault occurs when running `loadvm` having set `migrate_set_capability multifd on` from the monitor.
EDIT: also `savevm` segfaults.
Steps to reproduce:
1. Take a snapshot with `savevm test`
2. From the monitor run `migrate_set_capability multifd on`
3. Try to restore the snapshot with `loadvm test`
Additional information:
Sorry for not having triaged this much, I think it is worth reporting anyway.