vhost: disable reply-ack feature if IOMMU disabled

vhost: disable reply-ack feature if IOMMU disabled

If the application has disabled VIRTIO_F_IOMMU_PLATFORM, disable
VHOST_USER_PROTOCOL_F_REPLY_ACK protocol feature that is only
mandatory with IOMMU for now.

This is done to provide a way for the application to support
multiqueue with old Qemu versions (v2.7.0 to v2.9.0) that have
reply-ack feature broken.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>
Tested-by: Mark Kavanagh <mark.b.kavanagh@intel.com>
Acked-by: Mark Kavanagh <mark.b.kavanagh@intel.com>