optional mdns resolution (issue #3187)

Hello,

Could issue #3187 be solved as proposed here?

/etc/nsswitch.conf is a symbolic link to /var/run/nsswitch.conf

nsswitch.conf (without mdns) and nsswitch.mdns4 (with mdns4) configuration files sit in usr/config.

/usr/lib/openelec/nsswitch-setup copies the appropriate nsswitch configuration file from /usr/config to /var/run/nsswitch.conf, i.e. nsswitch.mdns4 if mdns4.conf and avahi.conf files exist in /storage/.cache/services, nsswitch.conf otherwise.

nsswitch.service runs nsswitch-setup after local-fs.target and before network.target.

I have succesfully tested this on my Raspberry Pi (even though I had to install nss-mdns via the testing package, because make release would not install it from packages/network/nss-mdns, maybe someone here could tell me what I am doing wrong).

Thank you for your attention, and regards,

Jean-Charles