docs(conventions): record that DTLS records chain like TLS's (#2535)

The Chained Records ruling on protocol-family-grouping.rst named DTLS as not
chaining; DTLS records sharing a datagram are now chained layers too.

Author: JarryShaw

docs/source/contributing/conventions/protocol-family-grouping.rst

@@ -230,12 +230,13 @@ are all ``False``; only ``frame.protochain`` matches them.
 Chained Records
 ~~~~~~~~~~~~~~~
 
-**TLS and SSLv2 records sharing a TCP segment are chained layers, not a list on one
-layer** (:issue:`2517`, :issue:`2567`): each record dissected after the first is the
-previous record's payload, so a TLS record's dynamic alias names its own version -- a
-``ServerHello`` then a ``ChangeCipherSpec`` read ``TCP:TLS 1.3:TLS 1.2`` -- and an SSLv2
-``CLIENT-HELLO`` then a ``CLIENT-MASTER-KEY`` read ``TCP:SSLv2:SSLv2``. DTLS does not
-chain: two DTLS records in one datagram read ``DTLS 1.2:Raw`` (:issue:`2535`).
+**TLS and SSLv2 records sharing a TCP segment, and DTLS records sharing a UDP datagram,
+are chained layers, not a list on one layer** (:issue:`2517`, :issue:`2567`,
+:issue:`2535`): each record dissected after the first is the previous record's payload,
+so a TLS or DTLS record's dynamic alias names its own version -- a ``ServerHello`` then a
+``ChangeCipherSpec`` read ``TCP:TLS 1.3:TLS 1.2``, and a DTLS 1.2 record then a DTLS 1.3
+unified-header record read ``UDP:DTLS 1.2:DTLS 1.3`` -- and an SSLv2 ``CLIENT-HELLO``
+then a ``CLIENT-MASTER-KEY`` read ``TCP:SSLv2:SSLv2``.
 
 .. _protocol-family-canonical-names: