librpc/rpc: add dcerpc_binding_handle_raw_call_in_*

librpc/rpc: add dcerpc_binding_handle_raw_call_in_*

The binding handle backend can support LIBNDR_FLAG_INCOMPLETE_BUFFER
with this change and implement the raw_call_in_send/recv functions
to get more data from the caller. The final chunk clears the
LIBNDR_FLAG_INCOMPLETE_BUFFER flag in the in_flags of raw_call_in_send().

If LIBNDR_FLAG_INCOMPLETE_BUFFER was indicated in the in_flags of raw_call_send()
the backend can deliver partial results to the caller,
in raw_call_recv() by specifying LIBNDR_FLAG_INCOMPLETE_BUFFER in the out_flags.
In that case the caller should not call TALLOC_FREE(subreq)
as there's more to come. The backend continues to delivers results by
raw_call_recv() and clears LIBNDR_FLAG_INCOMPLETE_BUFFER on the last chunk.

This will be used to implement support for DCERPC pipes.

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