LU-15317 llite: Add strided readahead to iotrace

LU-15317 llite: Add strided readahead to iotrace

We need to capture some additional parameters to correctly
understand the behavior of strided readahead.  Add these
parameters to the existing iotrace message.

test-parameters: trivial

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I7caddf9dfaf9ba5f2645d045d5a4a50562cc1b54
Reviewed-on: https://review.whamcloud.com/45888
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>