net/mlx5: Update log_max_qp value to FW max capability

log_max_qp in driver's default profile #2 was set to 18, but FW actually
supports 17 at the most - a situation that led to the concerning print
when the driver is loaded:
"log_max_qp value in current profile is 18, changing to HCA capabaility
limit (17)"

The expected behavior from mlx5_profile #2 is to match the maximum FW
capability in regards to log_max_qp. Thus, log_max_qp in profile #2 is
initialized to a defined static value (0xff) - which basically means that
when loading this profile, log_max_qp value  will be what the currently
installed FW supports at most.

Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>