qemu: remove unnecessary setting of tap device online state

The linkstate setting of an <interface> is only meant to change the
online status reported to the guest system by the emulated network
device driver in qemu, but when support for auto-creating tap devices
for <interface type='ethernet'> was added in commit 9717d6, a chunk of
code was also added to qemuDomainChangeNetLinkState() that sets the
online status of the tap device (i.e. the *host* side of the
interface) for type='ethernet'. This was never done for tap devices
used in type='bridge' or type='network' interfaces, nor was it done in
the past for tap devices created by external scripts for
type='ethernet', so we shouldn't be doing it now.

This patch removes the bit of code in qemuDomainChangeNetLinkState()
that modifies online status of the tap device.

src/qemu/qemu_hotplug.c

@@ -2324,21 +2324,6 @@ int qemuDomainChangeNetLinkState(virQEMUDriverPtr driver,
     if (ret < 0)
         goto cleanup;
 
-    if (virDomainNetGetActualType(dev) == VIR_DOMAIN_NET_TYPE_ETHERNET) {
-        switch (linkstate) {
-            case VIR_DOMAIN_NET_INTERFACE_LINK_STATE_UP:
-            case VIR_DOMAIN_NET_INTERFACE_LINK_STATE_DEFAULT:
-                if ((ret = virNetDevSetOnline(dev->ifname, true)) < 0)
-                    goto cleanup;
-                break;
-
-            case VIR_DOMAIN_NET_INTERFACE_LINK_STATE_DOWN:
-                if ((ret = virNetDevSetOnline(dev->ifname, false)) < 0)
-                    goto cleanup;
-                break;
-            }
-    }
-
     /* modify the device configuration */
     dev->linkstate = linkstate;