Add backward compatibility code to enable variable size WQEs only if the
user lib supports it.

Link: https://patch.msgid.link/r/1724042847-1481-6-git-send-email-selvin.xavier@broadcom.comSigned-off-by: Hongguang Gao <hongguang.gao@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>