LU-9679 osc: centralize handling of PTLRPCD_SET

LU-9679 osc: centralize handling of PTLRPCD_SET

Various places test if a given rqset is PTLRPCD_SET
and call either ptlrpcd_add_req() or ptlrpc_set_add_req()
depending on the result.

This can be unified by putting the test of PTLRPCD_SET in
ptlrpc_set_add_req(), and always calling that function.

This results in there being only one place that tests PTLRPCD_SET.

Linux-Commit: 6a587cd4c705 ("lustre: centralize handling of
	PTLRPCD_SET")

Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Mr NeilBrown <neilb@suse.com>
Change-Id: I879aa9ebb7e841dc2d1240a32d1c5d07e582e0b2
Reviewed-on: https://review.whamcloud.com/37603
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>