migration: allow qmp command migrate-start-postcopy for any postcopy

Allow migrate-start-postcopy for any postcopy type
Signed-off-by: NVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Message-id: 20180313180320.339796-11-vsementsov@virtuozzo.com

migration/migration.c

@@ -1022,7 +1022,7 @@ void qmp_migrate_start_postcopy(Error **errp)
 {
     MigrationState *s = migrate_get_current();
 
-    if (!migrate_postcopy_ram()) {
+    if (!migrate_postcopy()) {
         error_setg(errp, "Enable postcopy with migrate_set_capability before"
                          " the start of migration");
         return;