[PATCH] Babel: allow enabling link quality estimation manually

[Juliusz Chroboczek]

> +      <tag><label id="babel-link-quality">link quality <m/switch/</tag>
> +      If set, link quality estimation is performed on this interface.

There are multiple algorithms for estimating link quality, and the one
currently implemented by BIRD is ETX.  Hence, I feel that this should not
be a mere switch, but a selector with possible values

    none
    etx

in case we ever choose to implement some other LQ algorithm.

-- Juliusz