s3:rpc_client: don't mix layers and keep a reference to cli_state in the caller

s3:rpc_client: don't mix layers and keep a reference to cli_state in the caller

We should not rely on the backend to have a reference to the cli_state.
This will make it possible for the backend to set its cli_state reference
to NULL, when the transport is dead.

metze
(cherry picked from commit dc09b12681ea0e6d4c2b0f1c99dfeb1f23019c65)
(cherry picked from commit 1e2e47da82aeb249dce431541738a62cb139aebb)

Signed-off-by: Stefan Metzmacher <metze@samba.org>