network: don't add iptables rules for externally managed networks

This patch addresses https://bugzilla.redhat.com/show_bug.cgi?id=760442

When a network has any forward type other than route, nat or none, the
network configuration should be done completely external to libvirt -
libvirt only uses these types to allow configuring guests in a manner
that isn't tied to a specific host (all the host-specific information,
in particular interface names, port profile data, and bandwidth
configuration is in the network definition, and the guest
configuration only references it).

Due to a bug in the bridge network driver, libvirt was adding iptables
rules for networks with forward type='bridge' etc. any time libvirtd
was restarted while one of these networks was active.

This patch eliminates that error by only "reloading" iptables rules if
forward type is route, nat, or none.

src/network/bridge_driver.c

@@ -1470,14 +1470,22 @@ networkReloadIptablesRules(struct network_driver *driver)
     VIR_INFO("Reloading iptables rules");
 
     for (i = 0 ; i < driver->networks.count ; i++) {
-        virNetworkObjLock(driver->networks.objs[i]);
-        if (virNetworkObjIsActive(driver->networks.objs[i])) {
-            networkRemoveIptablesRules(driver, driver->networks.objs[i]);
-            if (networkAddIptablesRules(driver, driver->networks.objs[i]) < 0) {
+        virNetworkObjPtr network = driver->networks.objs[i];
+
+        virNetworkObjLock(network);
+        if (virNetworkObjIsActive(network) &&
+            ((network->def->forwardType == VIR_NETWORK_FORWARD_NONE) ||
+             (network->def->forwardType == VIR_NETWORK_FORWARD_NAT) ||
+             (network->def->forwardType == VIR_NETWORK_FORWARD_ROUTE))) {
+            /* Only the three L3 network types that are configured by libvirt
+             * need to have iptables rules reloaded.
+             */
+            networkRemoveIptablesRules(driver, network);
+            if (networkAddIptablesRules(driver, network) < 0) {
                 /* failed to add but already logged */
             }
         }
-        virNetworkObjUnlock(driver->networks.objs[i]);
+        virNetworkObjUnlock(network);
     }
 }