net: Drop vlan argument to qemu_new_net_client()

Since hubs are now used to implement the 'vlan' feature and the vlan
argument is always NULL, remove the argument entirely and update all net
clients that use qemu_new_net_client().

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
diff --git a/net/slirp.c b/net/slirp.c
index 7682ac7..85d6fb4 100644
--- a/net/slirp.c
+++ b/net/slirp.c
@@ -239,7 +239,7 @@
     }
 #endif
 
-    nc = qemu_new_net_client(&net_slirp_info, NULL, peer, model, name);
+    nc = qemu_new_net_client(&net_slirp_info, peer, model, name);
 
     snprintf(nc->info_str, sizeof(nc->info_str),
              "net=%s,restrict=%s", inet_ntoa(net),