devlink: implement dump selector for devlink objects show commands

devlink: implement dump selector for devlink objects show commands

Introduce a new helper dl_argv_parse_with_selector() to be used
by show() functions instead of dl_argv().

Implement it to check if all needed options got get commands are
specified. In case they are not, ask kernel for dump passing only
the options (attributes) that are present, creating sort of partial
key to instruct kernel to do partial dump.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>