Fix d2i_PrivateKey() to work as documented

Fix d2i_PrivateKey() to work as documented

d2i_PrivateKey() is documented to return keys of the type given as
first argument |type|, unconditionally.  Most specifically, the manual
says this:

> An error occurs if the decoded key does not match type.

However, when faced of a PKCS#8 wrapped key, |type| was ignored, which
may lead to unexpected results.

(cherry picked from commit b2952366dd0248bf35c83e1736cd203033a22378)

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/11888)