Convert dtls_write_records() to return the correct return values

Convert dtls_write_records() to return the correct return values

We now use standard record layer return values for this function. We
also convert the code to use RLAYERfatal instead of SSLfatal.

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)