qemu_hotplug: Fetch vhostuser ifname on hotplug

https://bugzilla.redhat.com/show_bug.cgi?id=1630164

Since 2a13a0a1 we are querying the vhostuser's interface name
when building qemu command line. However, we forgot to do so on
hotplug.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>

src/qemu/qemu_hotplug.c

@@ -1330,6 +1330,11 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
 
         if (!(charDevAlias = qemuAliasChardevFromDevAlias(net->info.alias)))
             goto cleanup;
+
+        if (virNetDevOpenvswitchGetVhostuserIfname(net->data.vhostuser->data.nix.path,
+                                                   &net->ifname) < 0)
+            goto cleanup;
+
         break;
 
     case VIR_DOMAIN_NET_TYPE_USER: