DECODER & ENCODER: Make sure to pass around the original selection bits

DECODER & ENCODER: Make sure to pass around the original selection bits

When decoding a key and asking the keymgmt to import the key data, it
was told that the key data includes everything.  This may not be true,
since the user may have specified a different selection, and some
keymgmts may want to be informed.

Our key decoders' export function, on the other hand, didn't care
either, and simply export anything they could, regardless.

In both cases, the selection that was specified by the user is now
passed all the way.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15934)