Move freeing of BIOs as late as possible

Move freeing of BIOs as late as possible

Calling SSL_free() will call BIO_free_all() on the rbio and wbio. We
keep references to the rbio and wbio inside the record layer object.
References to that object are held directly, as well as in fragment
retransmission queues. We need to ensure all record layer objects are
cleaned up before we call BIO_free_all() on rbio/wbio - otherwise the
"top" BIO may not have its reference count drop to 0 when BIO_free_all()
is called. This means that the rest of the BIOs in the chain don't get
freed and a memory leak can occur.

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)