LU-13180 lustre: reserve bit for RDMA-only memory RPC

This is reserved for RDMA-only memory integrated with Lustre.
The purpose of this bit is to:

1) disable short IO if memory is not dirextly addressie by CPU.
2) prevent CPU memory pages and RDMA memory pages merging into one RPC.

Test-Parameters: trivial
Change-Id: I148b269c5e7d7c52e760b20a6482c259407e0898
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/37383
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>