host port forward with qemu through libvirt in user-mode networking
the missing part from your configuration is described here: https://www.linux-kvm.org/page/Networking. You have to add another netdev with new address like so:
<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
.
.
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</devices>
<qemu:commandline>
<qemu:arg value='-netdev'/>
<qemu:arg value='user,id=mynet.0,net=10.0.10.0/24,hostfwd=tcp::22222-:22,hostfwd=tcp::8000-:8000'/>
<qemu:arg value='-device'/>
<qemu:arg value='e1000,netdev=mynet.0'/>
</qemu:commandline>
</domain>