rust: migration: implement ToMigrationState as part of impl_vmstate_bitsized

This is most likely desirable, and is the easiest way to migrate
a bit-sized value without peeking at the innards of the bilge crate.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed