block: implement .change_aio_ctx in child_of_bds

block: implement .change_aio_ctx in child_of_bds

bdrv_child_cb_change_aio_ctx() is identical to
bdrv_child_cb_can_set_aio_ctx(), as we only need
to recursively go on the parent bs.

Note: bdrv_child_try_change_aio_context() is not called by
anyone at this point.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20221025084952.2139888-6-eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>