net: cdc_ncm: export NCM Transfer Block (NTB) parameters

The mandatory GetNtbParameters control request is an important part of
the host <-> device protocol negotiation in CDC NCM (and CDC MBIM). It
gives device limits which the host must obey when configuring the
protocol aggregation variables. The driver will enforce this by
rejecting attempts to set any of the tunable variables to a value
which is not supported by the device.  Exporting the parameter block
helps userspace decide which values are allowed without resorting
to trial and error.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>