drbd atomic queue limits conversion

Hi Jens,

this is a standalone resend of the drbd queue limits conversion.
Philipp said Linbit has reviewed and tested it, and they'll hopefully
provide the formal tags for that in a bit.

Diffstat:
 drbd_main.c |   13 ++-
 drbd_nl.c   |  210 ++++++++++++++++++++++++++++--------------------------------
 2 files changed, 110 insertions(+), 113 deletions(-)