Create a dlts_write_records() function

Create a dlts_write_records() function

In preparation for moving the DTLS code to use the new write record layer
architecture we first restructure the code to create a dtls_write_records()
function that mirrors the functionality that the record layer will provide.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19424)