i40e/i40evf: Clean up feature flags

The feature flags list for i40e and i40evf is beginning to become pretty
massive.  I plan to add another 4 or so features to these drivers and
duplicating the flags for each and every flags list is becoming a bit
repetitive.

The primary change here is that we now build our features list around
hw_encap_features.  After that we assign that to vlan_features,
hw_features, and finally map that onto features.  In addition we end up
throwing features onto hw_encap_features that end up having no effect such
as the Rx offloads and SCTP_CRC.  However that should have no impact and
makes things a bit easier for us as hw_encap_features is one of the less
updated features maps available.

For i40evf I went through and sanity checked a few features as well.
Specifically RXCSUM was being set as a read-only feature which didn't make
much sense.  I have updated things so we can clear the NETIF_F_RXCSUM flag
since that is really a software feature and not a hardware one anyway so
disabling it is just a matter of ignoring the result from the hardware.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>