colo: Use file lock in primary_vm_do_failover()

Take the file lock since s->to_dst_file and s->rp_state.from_dst_file
may be changed in the migration thread.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20260302-colo_unit_test_multifd-v11-19-d653fb3b1d80@web.de
Signed-off-by: Fabiano Rosas <farosas@suse.de>

migration/colo.c

@@ -173,12 +173,14 @@ static void primary_vm_do_failover(void)
      * The s->rp_state.from_dst_file and s->to_dst_file may use the
      * same fd, but we still shutdown the fd for twice, it is harmless.
      */
+    WITH_QEMU_LOCK_GUARD(&s->qemu_file_lock) {
         if (s->to_dst_file) {
             qemu_file_shutdown(s->to_dst_file);
         }
         if (s->rp_state.from_dst_file) {
             qemu_file_shutdown(s->rp_state.from_dst_file);
         }
+    }
 
     old_state = failover_set_state(FAILOVER_STATUS_ACTIVE,
                                    FAILOVER_STATUS_COMPLETED);