properly handle stateless ICMP rules

fixes #2714

awall/model.lua

 --[[
 Base data model for Alpine Wall
-Copyright (C) 2012-2013 Kaarle Ritvanen
+Copyright (C) 2012-2014 Kaarle Ritvanen
 See LICENSE file for license details
 ]]--
 
@@ -264,7 +264,7 @@ function Rule:servoptfrags()
 	    elseif util.contains({58, 'ipv6-icmp', 'icmpv6'}, sdef.proto) then
 	       family = 'inet6'
 	       oname = 'icmpv6-type'
-	    elseif sdef.type then
+	    elseif sdef.type or sdef['reverse-type'] then
 	       self:error('Type specification not valid with '..sdef.proto)
 	    end
 
@@ -277,7 +277,11 @@ function Rule:servoptfrags()
 	       end
 	    end
 
-	    if sdef.type then opts = opts..' --'..oname..' '..sdef.type end
+	    if sdef.type then
+	       opts = opts..' --'..oname..' '..(
+		  self.reverse and sdef['reverse-type'] or sdef.type
+	       )
+	    end
 	    table.insert(res, {family=family, opts=opts})
 	 end
       end

json/services.json

@@ -82,8 +82,8 @@
     "ospf": { "proto": "ospf" },
     "pgsql": { "proto": "tcp", "port": 5432 },
     "ping": [
-      { "proto": "icmp", "type": 8 },
-      { "proto": "icmpv6", "type": 128 }
+      { "proto": "icmp", "type": 8, "reverse-type": 0 },
+      { "proto": "icmpv6", "type": 128, "reverse-type": 129 }
     ],
     "radius": [
       { "proto": "udp", "port": 1812 },