olsrd: splitting IPv6/4 configuration and start scripts

As mentioned by zioproto[1] 6and4 is badly broken, this patch will
use 2 different configuration and init scripts.

[1] https://github.com/openwrt-routing/packages/issues/16#issuecomment-32892327
olsrd: configuration sanity checks

* do not start in presence of the old /etc/config/olsrd
* use always use the appropriate IpVersion.
olsrd: avoid fake startup-error messages

Calling service_check too early may result in a false reading
olsrd: hotplug script works for IPv4 and IPv6

This should fix issue #16
olsrd: Merge branch 'olsrd_6and4' by Alessio Caiazza.