Don't re-announce services.

It is up to the browser to send a query before the TTL of a service is down to 0.
See '5.2.  Continuous Multicast DNS Querying' in rfc6762.
Add ANY to the record type enum.

ANY is needed for the responder to match on which queries to reply. Also swap
the dec<->hex mixup for AAAA record enum value.
Resend announcements after one second.

RFC 6762 8.3 requires initial service announcements to be resent at least a
second time with a 1 sec delay.
Set the cache flush bit on our announcements.

As we announce our own services, we set the cache flush bit (see rfc6762 10.2).
Add an enum for the dns record class field.
Send responses with IP TTL set to 255.

As suggested in rfc6762 11 the IP TTL should be set to 255 instead of the
default of 1 to work better with legacy systems.