Allow "tunnel" to be an encapsulation type.

tbsetup/ns2ir/tb_compat.tcl.in

 # -*- tcl -*-
 #
 # EMULAB-COPYRIGHT
-# Copyright (c) 2000-2006 University of Utah and the Flux Group.
+# Copyright (c) 2000-2006, 2008 University of Utah and the Flux Group.
 # All rights reserved.
 #
 
@@ -941,6 +941,9 @@ proc tb-set-link-encap {lanlink style} {
 	"alias" {
 	    set style "alias"
 	}
+	"tunnel" {
+	    set style "tunnel"
+	}
 	"veth" {
 	    set style "veth"
 	}
@@ -1115,6 +1118,9 @@ proc tb-set-vlink-emulation {style} {
 	"alias" {
 	    set style "alias"
 	}
+	"tunnel" {
+	    set style "tunnel"
+	}
 	"veth" {
 	    set style "veth"
 	}