Fix network hotplug to use device_add in QEMU

The initial boot of VMs uses -device for NICs where available. The
corresponding monitor command is device_add, but the network hotplug
code was still using device_del by mistake.

* src/qemu/qemu_driver.c: Use device_add for NIC hotplug where
  available

src/qemu/qemu_driver.c

@@ -7112,10 +7112,21 @@ static int qemudDomainAttachNetDevice(virConnectPtr conn,
         close(tapfd);
     tapfd = -1;
 
+    if (qemuCmdFlags & QEMUD_CMD_FLAG_DEVICE) {
+        if (!(nicstr = qemuBuildNicDevStr(net, vlan)))
+            goto try_remove;
+    } else {
         if (!(nicstr = qemuBuildNicStr(net, NULL, vlan)))
             goto try_remove;
+    }
 
     qemuDomainObjEnterMonitorWithDriver(driver, vm);
+    if (qemuCmdFlags & QEMUD_CMD_FLAG_DEVICE) {
+        if (qemuMonitorAddDevice(priv->mon, nicstr) < 0) {
+            qemuDomainObjExitMonitorWithDriver(driver, vm);
+            goto try_remove;
+        }
+    } else {
         if (qemuMonitorAddPCINetwork(priv->mon, nicstr,
                                      &guestAddr) < 0) {
             qemuDomainObjExitMonitorWithDriver(driver, vm);
@@ -7123,6 +7134,7 @@ static int qemudDomainAttachNetDevice(virConnectPtr conn,
         }
         net->info.type = VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI;
         memcpy(&net->info.addr.pci, &guestAddr, sizeof(guestAddr));
+    }
     qemuDomainObjExitMonitorWithDriver(driver, vm);
 
     ret = 0;