_mongoc_write_opmsg sets the write result's must_stop to true upon any error in sending the write command.
This bubbles up to mongoc_bulk_operation_execute here causing the entire bulk operation to fail.
Per the crud spec for the "ordered" option of bulk writes:
- If true, when a write fails, return without performing the remaining
- writes. If false, when a write fails, continue with the remaining writes, if any.
- Defaults to true.