net: Add support for XPS without sysfs being defined

This patch makes it so that we can support transmit packet steering without
sysfs needing to be enabled.  The reason for making this change is to make
it so that a driver can make use of the XPS even while the sysfs portion of
the interface is not present.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>