Fix use-after-free in BIO_C_SET_SSL callback

Fix use-after-free in BIO_C_SET_SSL callback

Since the BIO_SSL structure was renewed by `ssl_free(b)/ssl_new(b)`,
the `bs` pointer needs to be updated before assigning to `bs->ssl`.

Thanks to @suishixingkong for reporting the issue and providing a fix.

Closes #10539

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/11746)

(cherry picked from commit 73d6b4efe6835a6c97ce61df6bf339b0903e5b7a)