Query the device attributes for RDMA operations, including maximum
transfer size and maximum number of SGEs per RDMA WR, and report them
back to the userspace library.

Link: https://lore.kernel.org/r/20191121141509.59297-4-galpress@amazon.comSigned-off-by: NDaniel Kranzdorf <dkkranzd@amazon.com>
Reviewed-by: NYossi Leybovich <sleybo@amazon.com>
Signed-off-by: NGal Pressman <galpress@amazon.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>