network: better log message when network is inactive during reconnect

If the network isn't active during networkNotifyActualDevice(), we
would log an error message stating that the bridge device didn't
exist. This patch adds a check to see if the network is active, making
the logs more useful in the case that it isn't.

Partially resolves: https://bugzilla.redhat.com/1442700

(cherry picked from commit 7949de96)

src/network/bridge_driver.c

@@ -4682,6 +4682,13 @@ networkNotifyActualDevice(virDomainDefPtr dom,
     }
     netdef = network->def;
 
+    if (!virNetworkObjIsActive(network)) {
+        virReportError(VIR_ERR_OPERATION_INVALID,
+                       _("network '%s' is not active"),
+                       netdef->name);
+        goto error;
+    }
+
     /* if we're restarting libvirtd after an upgrade from a version
      * that didn't save bridge name in actualNetDef for
      * actualType==network, we need to copy it in so that it will be