LU-11951 ptlrpc: reset generation for old requests

LU-11951 ptlrpc: reset generation for old requests

all requests generated while the import is changing from
FULL to IDLE need to be moved to the new generation.

Change-Id: I59d9b92680c724132dba9c7315c26e9851c5d5d2
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/34221
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>