Pull NVMe fixes from Christoph:
"Three more fixes for 4.13 below:
- fix the incorrect bit for the doorbell buffer features (Changpeng Liu)
- always use a 4k MR page size for RDMA, to not get in trouble with
offset in non-4k page size systems (no-op for x86) (Max Gurtovoy)
- and a fix for the new nvme host memory buffer support to keep the
descriptor list DMA mapped when the buffer is enabled (me)"