LU-14138 ptlrpc: move more members in PTLRPC request into pill

LU-14138 ptlrpc: move more members in PTLRPC request into pill

Some data members in the data structure @ptlrpc_request can be
moved into the data structure @rep_capsule:
/** Request message - what client sent */
struct lustre_msg *rq_reqmsg;
/** Reply message - server response */
struct lustre_msg *rq_repmsg;
/** Fields that help to see if request and reply were swabbed */
__u32 rq_req_swab_mask;
__u32 rq_rep_swab_mask;

After these data structures are reconstructed, @rep_capsule can
be more common used and it makes pack and unpack sub requests
in a batch PtlRPC request for the coming batch metadata processing
more easily.

Lustre-change: https://review.whamcloud.com/40669
Lustre-commit: f75d2a1fc9b17b384bbcbc13bcb80ba10412cf29

Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: Ib6d942b79ebf1a444d63b55ad4bc94813cf947c7
Reviewed-on: https://review.whamcloud.com/46029
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>