IB/mlx5: Respect mlx5_core reserved GIDs

Reserved gids are taken by the mlx5_core, report smaller GID table
size to IB core.

Set mlx5_query_roce_port's return value back to int. In case of
error, return an indication. This rolls back some of the change
in commit 50f22fd8 ("IB/mlx5: Set mlx5_query_roce_port's return value to void")

Change set_roce_addr to use gid_set function, instead of directly
sending the command.

Signed-off-by: Ilan Tayari <ilant@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>