s3:rpc_client: implement bind time feature negotiation

s3:rpc_client: implement bind time feature negotiation

This is not strictly needed as we don't use any of the
optional features yet.

But it will make it easier to add bind time features we'll
actually use later.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>