i40e: Be much more verbose about what we can and cannot offload

commit f114dca2 upstream.

This change makes it so that we are much more robust about defining what we
can and cannot offload.  Previously we were just checking for the L4 tunnel
header length, however there are other fields we should be verifying as
there are multiple scenarios in which we cannot perform hardware offloads.

In addition the device only supports GSO as long as the MSS is 64 or
greater.  We were not checking this so an MSS less than that was resulting
in Tx hangs.

Change-ID: I5e2fd5f3075c73601b4b36327b771c64fcb6c31b
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Cc: Philipp Hahn <hahn@univention.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>