MFC r368167,r368187,r368203:

MFC r368167,r368187,r368203:

  r368167:
    NVME: Don't try to swap data on little endian machines.  These swapping
    functions violate BUSDMA contract - we cannot write to armed (by
    bus_dmamap_sync(PRE_..)) buffers. Remove them at least from little endian
    machines until a better solution will be developed.
  r368187:
    Unbreak r368167 in userland. Decorate unused arguments.
  r368203:
    Always use the __unused attribute even for potentially unused parameters.