linux: enable PERSISTENT_KEYRINGS and KEYS_REQUEST_CACHE
linux: enable PERSISTENT_KEYRINGS and KEYS_REQUEST_CACHE

PERSISTENT_KEYRINGS provides a register of persistent per-UID keyrings, useful for encrypting storage pools in stratis.
KEYS_REQUEST_CACHE enable temporary caching of the last request_key() result.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs