nvme-rdma: remove NVME_RDMA_MAX_SEGMENT_SIZE

NVME_RDMA_MAX_SEGMENT_SIZE is not used anywhere, zap it.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>