IB/mlx4: Report TSO capabilities

Report to the user area the TSO device capabilities, it includes the
max_tso size and the QP types that support it.

The TSO is applicable only when when of the ports is ETH and the device
supports it.

uresp logic around rss_caps is updated to fix a till-now harmless bug
computing the length of the structure to copy. The code did not handle the
implicit padding before rss_caps correctly. This is necessay to copy
tss_caps successfully.

Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>