Add dns_multicast_local to control mDNS operation

Add dns_multicast_local to control mDNS operation

Enable admin control over whether mDNS operates or not. Set the default
to OFF due to .arpa reverse-DNS requests causing a rise in traffic from
this feature even on networks without mDNS responders setup.

Also, polish cachemgr idns report to show for queued queries which
resolver type and query the entry is involving. mDNS can cause a queue
to exist as some lookups timeout on the mDNS resolvers.