network: Unconditionally initialize macmap when stopping virtual network

Since we can only ever have one reference to obj->macmap, rather
than only clearing obj->macmap during virNetworkObjUnrefMacMap
(e.g. virtual network from networkShutdownNetwork), let's just
unconditionally clear the obj->macmap to ensure that some future
change that created it's own reference to obj->macmap wouldn't
have that reference disappear if virNetworkObjDispose got called.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>

src/conf/virnetworkobj.c

@@ -125,8 +125,8 @@ virNetworkObjSetMacMap(virNetworkObjPtr obj,
 void
 virNetworkObjUnrefMacMap(virNetworkObjPtr obj)
 {
-    if (!virObjectUnref(obj->macmap))
-        obj->macmap = NULL;
+    virObjectUnref(obj->macmap);
+    obj->macmap = NULL;
 }