LU-6349 idl: clean up and document ptlrpc structures

LU-6349 idl: clean up and document ptlrpc structures

Miscellaneous cleanups for wire-related structures found during the
Lustre protocol documentation project.

Remove obsolete and unused since 2.3 OBD_QC_CALLBACK RPC.

Move definition of constants used by lustre_msg_v2 and ptlrpc_body
fields to immediately before their respective structures.

Add comments for struct members for lustre_msg_v2, ptlrpc_body_v3,
ldlm_request, and obd_statfs.

Rename RQF_MDS_INTENT_CLOSE to RQF_MDS_CLOSE_INTENT to make it more
easily found with RQF_MDS_CLOSE.  Rename mdt_intent_close_client()
and mdc_intent_close_pack() to mdt_close_intent_client() and
mdc_close_intent_pack() to match.

Rename RQF_LDLM_GL_DESC_CALLBACK to RQF_LDLM_GL_CALLBACK_DESC to make
it match RQF_LDLM_FL_CALLBACK and RQF_LDLM_BL_CALLBACK.

Remove unused MSG_OP_FLAG_MASK, MSG_OP_FLAG_SHIFT, MSG_GEN_FLAG_MASK.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I21be2ec0aacef9965ff9c835174b5b017b3ebbe5
Reviewed-on: https://review.whamcloud.com/17830
Reviewed-by: Ben Evans <bevans@cray.com>
Tested-by: Jenkins
Reviewed-by: Steve Guminski <stephenx.guminski@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>