natd fw punch rule leak found (and fix)

[Flemming Kraglund]

Ups, there you go when not testing your last optimization, it is
required that a fw rule number is allocated for partial connections
so the fix is just:
in libalias/alias_db.c in PunchFWHole add the following after the
initial packetAliasMode test:
	ClearFWHole(link);

/FK