Add Chacha20-Poly1305 as a KTLS cipher suite.

[jhb]

Summary

Chacha20-Poly1305 for TLS is an AEAD cipher suite for both TLS 1.2 and
TLS 1.3 (RFCs 7905 and 8446). For both versions, Chacha20 uses the
server and client IVs as implicit nonces xored with the record
sequence number to generate the per-record nonce matching the
construction used with AES-GCM for TLS 1.3.

Test Plan

Tested with pure software openssl s_client on a host and KTLS-enabled openssl s_server in a VM using chacha20 ciphers with both TLS 1.2 and TLS 1.3.

[jhb]

• Rebase.