ibmvnic: Add ethtool private flag for driver-defined queue limits

ibmvnic: Add ethtool private flag for driver-defined queue limits

When choosing channel amounts and ring sizes, the maximums in the
ibmvnic driver are defined by the virtual i/o server management
partition. Even though they are defined as maximums, the client
driver may in fact successfully request resources that exceed
these limits, which are mostly dependent on a user's hardware

With this in mind, provide an ethtool flag that when enabled will
allow the user to request resources limited by driver-defined
maximums instead of limits defined by the management partition.
The driver will try to honor the user's request but may not allowed
by the management partition. In this case, the driver requests
as close as it can get to the desired amount until it succeeds.

Signed-off-by: Thomas Falcon <tlfalcon@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>