idpf: refactor remaining virtchnl messages

This takes care of RSS/SRIOV/MAC and other misc virtchnl messages. This
again is mostly mechanical.

In absence of an async_handler for MAC filters, this will simply
generically report any errors from idpf_vc_xn_forward_async. This
maintains the existing behavior. Follow up patch will add an async
handler for MAC filters to remove bad filters from our list.

While we're here we can also make the code much nicer by converting some
variables to auto-variables where appropriate. This makes it cleaner and
less prone to memory leaking.

There's still a bit more cleanup we can do here to remove stuff that's
not being used anymore now; follow-up patches will take care of loose
ends.

Tested-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>