IB/mlx5: Use unlimited rate when static rate is not supported

IB/mlx5: Use unlimited rate when static rate is not supported

Before the change, if the user passed a static rate value different
than zero and the FW doesn't support static rate,
it would end up configuring rate of 2.5 GBps.

Fix this by using rate 0; unlimited, in cases where FW
doesn't support static rate configuration.

Cc: <[email protected]> # 3.10
Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Reviewed-by: Majd Dibbiny <[email protected]>
Signed-off-by: Danit Goldberg <[email protected]>
Signed-off-by: Leon Romanovsky <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>