qom: Make object_property_set_qobject()'s input visitor strict

Commit 240f64b made all qobject input visitors created outside tests
strict, except for the one in object_property_set_qobject(). That one
was left behind only because Eric couldn't spare the time to figure
out whether making it strict would break anything, with a TODO
comment. Time to resolve it.

Strict makes a difference only for otherwise successful visits of QAPI
structs or unions. Let's examine what the callers of
object_property_set_qobject() visit:

* object_property_set_str(), object_property_set_bool(),
object_property_set_int() visit a QString, QBool, QInt,
respectively. Strictness can't matter.

* qmp_qom_set visits its @value argument. Comes straight from QMP and
can be anything ('any' in the QAPI schema). Strictness matters when
the property's set() method visits a struct or union QAPI type.

No such methods exist, thus switching to strict can't break
anything.

If we acquire such methods in the future, we'll *want* the visitor
to be strict, so that unexpected members get rejected as they should
be.

Switch to strict.

Backports commit 05601ed2de60df0e344d6b783a6bc0c1ff2b5d1f from qemu

qemu/qom/qom-qobject.c

@@ -22,8 +22,7 @@ void object_property_set_qobject(struct uc_struct *uc, Object *obj, QObject *val
                                  const char *name, Error **errp)
 {
     Visitor *v;
-    /* TODO: Should we reject, rather than ignore, excess input? */
-    v = qobject_input_visitor_new(value, false);
+    v = qobject_input_visitor_new(value, true);
     object_property_set(uc, obj, v, name, errp);
     visit_free(v);
 }