IB/core: Improve ib_map_mr_sg() documentation

Document that ib_map_mr_sg() is able to map physically discontiguous
sg-lists as a single MR. Change IB_MR_TYPE_SG_GAPS_REG into
IB_MR_TYPE_SG_GAPS.
Signed-off-by: NBart Van Assche <bart.vanassche@sandisk.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NSagi Grimberg <sagi@rimberg.me>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

drivers/infiniband/core/verbs.c

@@ -1811,13 +1811,13 @@ EXPORT_SYMBOL(ib_set_vf_guid);
  *
  * Constraints:
  * - The first sg element is allowed to have an offset.
- * - Each sg element must be aligned to page_size (or physically
- *   contiguous to the previous element). In case an sg element has a
- *   non contiguous offset, the mapping prefix will not include it.
+ * - Each sg element must either be aligned to page_size or virtually
+ *   contiguous to the previous element. In case an sg element has a
+ *   non-contiguous offset, the mapping prefix will not include it.
  * - The last sg element is allowed to have length less than page_size.
  * - If sg_nents total byte length exceeds the mr max_num_sge * page_size
  *   then only max_num_sg entries will be mapped.
- * - If the MR was allocated with type IB_MR_TYPE_SG_GAPS_REG, non of these
+ * - If the MR was allocated with type IB_MR_TYPE_SG_GAPS, none of these
  *   constraints holds and the page_size argument is ignored.
  *
  * Returns the number of sg elements that were mapped to the memory region.