Removed 'use by clients' and 'use by server' sections, which had only
been discussing how the Meta-RR is handled.  But Meta-RR isn't the main
point of the document (Meta-RR is just discovery of DNSoD support).  We
do need to explain what clients and what servers should do, but after
we nail down if multiplexing is acceptable to the WG, and if we want
discovery to work in-band or just by sending DTLS ClientHello.

Adjusted SRV to use CHAOS (RFC4892) which Tiru and Prashanth had already
documented.

Added text about MTU, TCP queries, and ideas for a shim to avoid TCP.