Add a custom "X-forwarded-for" header name

For breadth of the iRules vs Local Traffic Policy conversation...I tend to disagree with the generic advice of policy > iRules. I know policies are more performant (but marginal, YMMV), and if you can use policies over iRules that's fine, but my personal rule of thumb (not F5 official best practices or recommendations) on policies is to use them ONLY IF:

1. I don't need any Tcl in them
2. I don't have any iRules touching the same virtual servers
3. My use for iRules is very limited globally
4. I'm very good at documenting the lines of mgmt/control between the logic in native objects vs iRules
5. I own the iRules AND the policies