LU-15435 ptlrpc: unregister reply buffer on rq_err

LU-15435 ptlrpc: unregister reply buffer on rq_err

Unregister reply buffer on rq_err and prevent a late reply from
modifying request flags in INTERPRET state.

Fixes: cefabee52586 ("LU-15112 mgc: do not ignore target registration failure")
HPE-bug-id: LUS-10717

Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Signed-off-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Change-Id: I0106e3fd5443c1292c103247cdbf6122f91922e8
Reviewed-on: https://review.whamcloud.com/46132
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>