linux 6.3 compat: needs REQ_PREFLUSH | REQ_OP_WRITE

Modify bio_set_flush() so if kernel version is >= 4.10, flags
REQ_PREFLUSH and REQ_OP_WRITE are set together.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Youzhong Yang <yyang@mathworks.com>
Closes #14695