iavf: Add framework to enable ethtool RSS config

Add the virtchnl message interface to VF, so that VF can request RSS
input set(s) based on PF's capability.

This framework allows ethtool RSS config support on the VF driver.

Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>