net/virtio: revert forcing IOVA as VA mode for virtio-user

net/virtio: revert forcing IOVA as VA mode for virtio-user

This patch removes the simplification in Virtio descriptors
handling, where their buffer addresses are IOVAs for Virtio
PCI devices, and VA-only for Virtio-user devices, which
added a requirement on Virtio-user that it only supported
IOVA as VA.

This change introduced a regression for applications using
Virtio-user and other physical PMDs that require IOVA as PA
because they don't use an IOMMU.

This patch reverts to the old behaviour, but needed to be
reworked because of the refactoring that happened in v21.02.

Fixes: 17043a2909bb ("net/virtio: force IOVA as VA mode for virtio-user")
Cc: stable@dpdk.org
Reported-by: Olivier Matz <olivier.matz@6wind.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Tested-by: Olivier Matz <olivier.matz@6wind.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>