avahi: samba service cosmetics

When samba is built with avahi support the server name is advertised in UPPERCASE as samba forces this when setting-up avahi via dbus. If we disable avahi support in samba and include a samba.service file with avahi the hostname is correctly advertised as the user entered it; e.g. "OpenELEC" not "OPENELEC" - we can also use a tweaked samba.service so that Mac users with an AppleTV see the AppleTV icon in Finder.app instead of a generic server icon.