Move the vf to VST 802.1ad mode (mlx4 VST QinQ mode) by setting vf vlan
protocol to 802.1ad.
VST 802.1ad mode in mlx4, is used for STAG strip/insertion by PF, while
the CTAG is set by the VF.
Read current vlan protocol as part of the vf configuration state.

Upon setting vf vlan protocol to 802.1ad, we use a mechanism of handshake
to verify that both the vf and the pf driver version support it.
The handshake uses the command QUERY_FUNC_CAP:
- The vf sets a pre-defined support bit in input modifier.
- A pf that supports the feature sends the request to the vf through a
  pre-defined field in the output mailbox.
- In case vf does not support the feature, the pf will fail the control
  command (in this case, IP link tool command to set the vf vlan
  protocol to 802.1ad).

No change in VST 802.1Q mode.
Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>