Add a prepare for encryption step

Add a prepare for encryption step

This applies any mac that might be necessary, ensures that we have
enough space in the WPACKET to perform the encryption and sets up the
SSL3_RECORD ready for that encryption.

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19343)