Move numwpipes in the write record layer

Move numwpipes in the write record layer

We retain a numwpipes for now in the old record layer structure for use
by DTLS. This will eventually be removed when DTLS moves over to the new
way of doing things.

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19198)