drbd: move UAPI headers to include/uapi/linux/

drbd: move UAPI headers to include/uapi/linux/

drbd.h and drbd_limits.h contain only type definitions, enums, and
constants shared between kernel and userspace. These should be part of
UAPI.

Split the genl_api header into two: the genlmsghdr and the enums are
UAPI, the rest stays there for now (it will be removed by one of the
next commits in this series).

drbd_config.h is clearly DRBD-internal, so move it there.

Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20260506124541.1951772-2-christoph.boehmwalder@linbit.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>