net/virtio: pack virtio HW struct

net/virtio: pack virtio HW struct

This patch improves the virtio_hw struct packing,
going from 88 down to 80 bytes with a 6 bytes hole in
the end of the first cacheline. Fields only used in the
slow path are placed in the end, so that hot path only
uses the first cacheline.

The patch also changes booleans fields to uint8_t type, and
fix inconsistencies in their assignments.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>