dnssd should not use plug as NonOlsrIf; it should only use one iface for...

... this option: ap or secAp.

This should fix the dnssd bug we saw at AMC, which causes massive instability with wireless ad-hoc links.

Test in conjunction with this: https://github.com/opentechinstitute/olsrd/pull/4

For testing, the nodes at LTS should be reflashed with this change, and tested in a configuration similar to AMC MagicNet, with both wired and wireless mesh links.

Preliminary testing indicates success in fixing this bug.