rust: migration: allow passing ParentField<> to vmstate_of!

The common superclass for devices could have its own migration state;
for it to be included in the subclass's VMState, ParentField<> must
implement the VMState trait.

Reported-by: Chen Miao <chenmiao@openatom.club>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2 files changed