LU-13899 tgt: drop old epoch request

LU-13899 tgt: drop old epoch request

Do not send -ESTALE back to the client
in case process_req_last_xid() detects
an old epoch request. Just drop reply
instead, otherwise -ESTALE may confuse
the client and have it accept an error
not attempting to resend the request.

Fixes: c1d465de13 ("LU-6655 ptlrpc: skip delayed replay requests")
HPE-bug-id: LUS-9097
Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Change-Id: I1a9ebc637f1357ca0027adbb6bb706287f4b5f4f
Reviewed-on: https://review.whamcloud.com/39612
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>