ethtool: Fail number of channels change when it conflicts with rxnfc

Similar to what we do with the hash indirection table [1], when network
flow classification rules are forwarding traffic to channels greater
than the requested number of channels, fail the operation.
Without this, traffic could be directed to channels which no longer
exist (dropped) after changing number of channels.

[1] commit d4ab4286

 ("ethtool: correctly ensure {GS}CHANNELS doesn't conflict with GS{RXFH}")

Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Link: https://lore.kernel.org/r/20221106123127.522985-1-gal@nvidia.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>