qemu: check actual netdev type rather than config netdev type during init

This resolves:

   https://bugzilla.redhat.com/show_bug.cgi?id=1012824
   https://bugzilla.redhat.com/show_bug.cgi?id=1012834

Note that a similar problem was reported in:

   https://bugzilla.redhat.com/show_bug.cgi?id=827519

but the fix only worked for <interface type='hostdev'>, *not* for
<interface type='network'> where the network itself was a pool of
hostdevs.

The symptom in both cases was this error message:

   internal error: Unable to determine device index for network device

In both cases the cause was lack of proper handling for netdevs
(<interface>) of type='hostdev' when scanning the netdev list looking
for alias names in qemuAssignDeviceNetAlias() - those that aren't
type='hostdev' have an alias of the form "net%d", while those that are
hostdev use "hostdev%d". This special handling was completely lacking
prior to the fix for Bug 827519 which was:

When searching for the highest alias index, libvirt looks at the alias
for each netdev and if it is type='hostdev' it ignores the entry. If
the type is not hostdev, then it expects the "net%d" form; if it
doesn't find that, it fails and logs the above error message.

That fix works except in the case of <interface type='network'> where
the network uses hostdev (i.e. the network is a pool of VFs to be
assigned to the guests via PCI passthrough). In this case, the check
for type='hostdev' would fail because it was done as:

     def->net[i]->type == VIR_DOMAIN_NET_TYPE_HOSTDEV

(which compares what was written in the config) when it actually
should have been:

    virDomainNetGetActualType(def->net[i]) == VIR_DOMAIN_NET_TYPE_HOSTDEV

(which compares the type of netdev that was actually allocated from
the network at runtime).

Of course the latter wouldn't be of any use if the netdevs of
type='network' hadn't already acquired their actual network connection
yet, but manual examination of the code showed that this is never the
case.

While looking through qemu_command.c, two other places were found to
directly compare the net[i]->type field rather than getting actualType:

* qemuAssignDeviceAliases() - in this case, the incorrect comparison
  would cause us to create a "net%d" alias for a netdev with
  type='network' but actualType='hostdev'. This alias would be
  subsequently overwritten by the proper "hostdev%d" form, so
  everything would operate properly, but a string would be
  leaked. This patch also fixes this problem.

* qemuAssignDevicePCISlots() - would defer assigning a PCI address to
  a netdev if it was type='hostdev', but not for type='network +
  actualType='hostdev'. In this case, the actual device usually hasn't
  been acquired yet anyway, and even in the case that it has, there is
  no practical difference between assigning a PCI address while
  traversing the netdev list or while traversing the hostdev
  list. Because changing it would be an effective NOP (but potentially
  cause some unexpected regression), this usage was left unchanged.

src/qemu/qemu_command.c

@@ -817,7 +817,8 @@ qemuAssignDeviceNetAlias(virDomainDefPtr def, virDomainNetDefPtr net, int idx)
         for (i = 0; i < def->nnets; i++) {
             int thisidx;
 
-            if (def->nets[i]->type == VIR_DOMAIN_NET_TYPE_HOSTDEV) {
+            if (virDomainNetGetActualType(def->nets[i])
+                == VIR_DOMAIN_NET_TYPE_HOSTDEV) {
                 /* type='hostdev' interfaces have a hostdev%d alias */
                continue;
             }
@@ -987,8 +988,9 @@ qemuAssignDeviceAliases(virDomainDefPtr def, virQEMUCapsPtr qemuCaps)
             /* type='hostdev' interfaces are also on the hostdevs list,
              * and will have their alias assigned with other hostdevs.
              */
-            if ((def->nets[i]->type != VIR_DOMAIN_NET_TYPE_HOSTDEV) &&
-                (qemuAssignDeviceNetAlias(def, def->nets[i], i) < 0)) {
+            if (virDomainNetGetActualType(def->nets[i])
+                != VIR_DOMAIN_NET_TYPE_HOSTDEV &&
+                qemuAssignDeviceNetAlias(def, def->nets[i], i) < 0) {
                 return -1;
             }
         }