qemu: Actually clear bandwidth settings

The virDomainSetInterfaceParameters implementation in qemu over
VIR_DOMAIN_AFFECT_CONFIG doesn't work as expected. When trying to
clear out the bandwidth settings for an interface, it has no
actual effect:

    virsh # domiftune --config $domain $interface
    inbound.average: 100
    inbound.peak   : 0
    inbound.burst  : 0
    outbound.average: 10
    outbound.peak  : 0
    outbound.burst : 0

    virsh domiftune --config $domain $interface 0 0

    virsh # domiftune --config $domain $interface
    inbound.average: 100
    inbound.peak   : 0
    inbound.burst  : 0
    outbound.average: 10
    outbound.peak  : 0
    outbound.burst : 0

But according to virsh man page:

    To clear inbound or outbound settings, use --inbound or
    --outbound respectfully with average value of zero.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_driver.c

@@ -9983,11 +9983,15 @@ qemuDomainSetInterfaceParameters(virDomainPtr dom,
                 VIR_FREE(persistentNet->bandwidth->in);
                 persistentNet->bandwidth->in = bandwidth->in;
                 bandwidth->in = NULL;
+            } else  if (inboundSpecified) {
+                VIR_FREE(persistentNet->bandwidth->in);
             }
             if (bandwidth->out) {
                 VIR_FREE(persistentNet->bandwidth->out);
                 persistentNet->bandwidth->out = bandwidth->out;
                 bandwidth->out = NULL;
+            } else if (outboundSpecified) {
+                VIR_FREE(persistentNet->bandwidth->out);
             }
         }