When exporting/importing decoded keys do not use 0 as selection

When exporting/importing decoded keys do not use 0 as selection

When decoding 0 as the selection means to decode anything
you get.

However when exporting and then importing the key data 0 as
selection is not meaningful.
So we set it to OSSL_KEYMGMT_SELECT_ALL to make the export/import
function export/import everything that we have decoded.

Fixes #21493

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/21519)