Define port handling helpers what don't rely on internal_flags.
Have __devlink_nl_pre_doit() to accept the flags as a function arg and
make devlink_nl_pre_doit() a wrapper helper function calling it.
Introduce new helpers devlink_nl_pre_doit_port() and
devlink_nl_pre_doit_port_optional() to be used by split ops in follow-up
patch.

Note that the function prototypes are temporary until the generated ones
will replace them in a follow-up patch.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230811155714.1736405-4-jiri@resnulli.usSigned-off-by: Jakub Kicinski <kuba@kernel.org>