dcerpc.idl: replace dcerpc_response._pad with a uint8 reserved

dcerpc.idl: replace dcerpc_response._pad with a uint8 reserved

typedef struct {
        uint32 alloc_hint;
        uint16 context_id;
        uint8 cancel_count;
        [value(0)] uint8 reserved;
        [flag(NDR_REMAINING)] DATA_BLOB stub_and_verifier;
} dcerpc_response;

- the generic dcerpc header has a size of 16 bytes

- alloc_hint, context_id, cancel_count and reserved are 8 bytes together

So stub_and_verifier is 8 byte aligned at offset 24.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>