xen/netback: Add module alias for autoloading

Add xen-backend:vif module alias to the xen-netback module. This allows
automatic loading of the module.

Signed-off-by: Bastian Blank <waldi@debian.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/net/xen-netback/netback.c

@@ -1743,3 +1743,4 @@ failed_init:
 module_init(netback_init);
 
 MODULE_LICENSE("Dual BSD/GPL");
+MODULE_ALIAS("xen-backend:vif");