RDMA/mlx4: Ensure that maximal send/receive SGE less than supported by HW

In calculating the global maximum number of the Scatter/Gather elements
supported, the following four maximum parameters must be taken into
consideration: max_sg_rq, max_sg_sq, max_desc_sz_rq and max_desc_sz_sq.

However instead of bringing this complexity to query_device, which still
won't be sufficient anyway (the calculations are dependent on QP type),
the safer approach will be to restore old code, which will give us 32
SGEs.

Fixes: 33023fb8 ("IB/core: add max_send_sge and max_recv_sge attributes")
Reported-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>