drbd: clean up UAPI headers

drbd: clean up UAPI headers

Commit b1798910fc7f ("drbd: move UAPI headers to include/uapi/linux/")
broke compilation on targets without a hosted libc:

  ./usr/include/linux/drbd.h:18:10: fatal error: sys/types.h: No such
  file or directory

The underlying issue is that there were some constructs left over in
those headers that don't belong in uapi.

Drop the __KERNEL__-gated split in drbd.h. The !__KERNEL__ branch pulls
in <sys/types.h>, <sys/wait.h> and <limits.h> for symbols that the
header does not actually reference; they were carried over from when
this lived in include/linux/.
Replace <asm/types.h> and the entire #ifdef block with the standard
UAPI combo <linux/types.h> + <asm/byteorder.h>, which provides
__u32/__u64/__s32 and __{LITTLE,BIG}_ENDIAN_BITFIELD in both kernel
and userspace contexts.

drbd_limits.h references some enum values and the DRBD_PROT_C define
from drbd.h, but does not include it. Add the missing include while
we're here.

Drop the unprefixed DEBUG_RANGE_CHECK from drbd_limits.h. It has no
in-kernel users and pollutes the userspace namespace.

Switch the drbd.h and drbd_limits.h include guards to the _UAPI_LINUX_*
convention already used by drbd_genl.h.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202605101346.V2wwJqv1-lkp@intel.com/
Fixes: b1798910fc7f ("drbd: move UAPI headers to include/uapi/linux/")
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://patch.msgid.link/20260513110343.3170338-1-christoph.boehmwalder@linbit.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>