Merge branch 'ethtool-set_channels-add-a-few-more-checks'

Jakub Kicinski says:

====================
ethtool: set_channels: add a few more checks

There seems to be a few more things we can check in the core before
we call drivers' ethtool_ops->set_channels. Adding the checks to
the core simplifies the drivers. This set only includes changes
to the NFP driver as an example.

There is a small risk in the first patch that someone actually
purposefully accepts a strange configuration without RX or TX
channels, but I couldn't find such a driver in the tree.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>