MINOR: ring: make the parse function automatically set the handler/release

MINOR: ring: make the parse function automatically set the handler/release

ring_attach_cli() is called by the keyword parsing function to dump a
ring to the CLI. It can only work with a specific handler and release
function. Let's make it set them appropriately instead of having the
caller know these functions. This way adding a command to dump a ring
is as simple as declaring a parsing function calling ring_attach_cli().