Remove '\n' from vhostuser ifname

Issue

• After run virsh dumpxml, it looks like the xml contains improperly a new line character.

...snip...
<interface type='vhostuser'>
<mac address='(mac address)'/>
<source type='unix' path='(socket file path)' mode='server'/>
<target dev='f1234567890-ff <------- invalid a new line character 
'/>
<model type='virtio'/>
<driver rx_queue_size='1024' tx_queue_size='1024'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
...snip...