Call colo_release_ram_cache() after multifd threads terminate

The multifd threads still may access the colo cache, so release it
only after they terminate.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Link: https://lore.kernel.org/qemu-devel/20260302-colo_unit_test_multifd-v11-9-d653fb3b1d80@web.de
Signed-off-by: Fabiano Rosas <farosas@suse.de>

migration/colo.c

@@ -949,7 +949,4 @@ void coroutine_fn colo_incoming_co(void)
     /* Wait checkpoint incoming thread exit before free resource */
     qemu_thread_join(&th);
     bql_lock();
-
-    /* We hold the global BQL, so it is safe here */
-    colo_release_ram_cache();
 }

migration/migration.c

@@ -454,6 +454,9 @@ void migration_incoming_state_destroy(void)
      * BQL and retake unconditionally.
      */
     assert(bql_locked());
+    if (migrate_colo()) {
+        colo_release_ram_cache();
+    }
     qemu_loadvm_state_cleanup(mis);
 
     if (mis->to_src_file) {