Add missing argname for keymgmt_gettable_params and keymgmt_settable_params prototypes

Add missing argname for keymgmt_gettable_params and keymgmt_settable_params prototypes

For some reason `keymgmt_gettable_params` and `keymgmt_settable_params`
seem to be the only prototypes in `core_dispatch.h` without named
arguments.

This is annoying if `core_dispatch.h` is being parsed to extract
information and also for developers who would like the header to be
self-contained, without having to refer to the documentation every time
to check what is supposed to be passed.

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14950)