IB/mlx5: Enable Eth VFs to query their min-inline value for user-space

For some mlx5 HW models (CX4, CX4Lx), the VF driver needs to put part
of the packet headers on the TX descriptor so the e-switch can do proper
matching and steering. This is called "min-inline", it's advertized to
the VF by the FW and also enforced on them by the HW, such that if they
don't obey, their packets are dropped.

SRIOV VF libmlx5 instances should take into account the min-inline
value of their vports. For that end, we provide this value through
the vendor response part of init_ucontext command.

The min inline value is reported in a way which will let newer libmlx5
instances realize that they are running over an older kernel and act
accordingly (e.g apply some educated guess).

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>