lantiq: use ActualNetDataRate for speed reporting

lantiq: use ActualNetDataRate for speed reporting

Switch to Actual Net Data Rate (ACTNDR) for speed reporting on lantiq VDSL modems

Refer to ITU-T G.997.1 chapter 7.5.2.8

Independent whether retransmission is used or not in a given transmit direction:
-   In L0 state, this parameter reports the Net Data Rate (as specified in G.992.3, G.992.5 or G.993.2) at which the bearer channel is operating.
-   In  L2 state, the parameter contains the Net Data Rate (as specified in G.992.3, G.992.5 or G.993.2) in the previous L0 state.

Signed-off-by: Jeroen Peelaerts <jeroen.peelaerts@gmail.com>
Reviewed-by: Andre Heider <a.heider@gmail.com>
(cherry picked from commit 4f27ea7c33447f4b0c8e577509726927916b9625)