nixos/lighttpd: add missing modules to allKnownModules

The output of ./configure shows all modules/plugins, both enabled and
disabled. With this info we can finally build the _complete_ list of
modules. We were missing these:

  mod_authn_gssapi
  mod_authn_ldap
  mod_geoip

(I hit this as I was building lighttpd with ldap support and the NixOS
module said ldap was unsupported, due to these missing entries in
allKnownModules.)