LU-11117 ptlrpc: don't zero request handle

LNet can retransmit a request at any time if it isn't replied.
The ptlrpc_resend_req zero the request handle and ptlrpc_send_rpc
set it. If retransmission happen with zeroed handle, the client
can't find a valid export by handle and set rq_export to NULL and
reply with ENOTCONN. A server evict client with this error.

client (nid x.x.x.x@tcp) returned error from blocking AST
(req status -107 rc -107), evict it

Signed-off-by: Alexander Boyko <c17825@cray.com>
Cray-bug-id: LUS-6037
Change-Id: I198666d386fea99b46994f965c1519acb5743d75
Reviewed-on: https://review.whamcloud.com/32781


Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>