RDMA/bnxt_re: Restrict the max_gids to 256

Some adapters report more than 256 gid entries. Restrict it to 256 for
now.

Fixes: 1ac5a404("RDMA/bnxt_re: Add bnxt_re RoCE driver")
Link: https://lore.kernel.org/r/1598292876-26529-6-git-send-email-selvin.xavier@broadcom.com


Signed-off-by: Naresh Kumar PBS <nareshkumar.pbs@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>