zbd: add missing client/server support for option max_open_zones

Ensure that we convert the max_open_zones option for client/server.

Use __cpu_to_le32()/__le32_to_cpu() rather than
cpu_to_le32()/le32_to_cpu(), since max_open_zones is defined
as int rather than unsigned int in thread_options.h.

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>