net/virtio: enable indirect descriptors feature

net/virtio: enable indirect descriptors feature

Virtio indirect descriptors are supported by the data-path
but the feature bit is never set during feature negociation.

This patch simply adds VIRTIO_RING_F_INDIRECT_DESC back to
the supported features bit mask, hence enabling the use of
indirect descriptors when the feature is negociated with the
device.

Signed-off-by: Pierre Pfister <ppfister@cisco.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>