sphinx: Actually use the pad stream to generate the packet

We flipped two buffers and were not actually using the chacha20 stream.

common/sphinx.c

@@ -425,7 +425,7 @@ struct onionpacket *create_onionpacket(
 	/* Note that this is just hop_payloads: the rest of the packet is
 	 * overwritten below or above anyway. */
 	generate_key(padkey, "pad", 3, sp->session_key);
-	generate_cipher_stream(stream, padkey, ROUTING_INFO_SIZE);
+	generate_cipher_stream(packet->routinginfo, padkey, ROUTING_INFO_SIZE);
 
 	generate_header_padding(filler, sizeof(filler), sp, params);
 

tests/test_pay.py

@@ -2479,7 +2479,7 @@ def test_createonion_rpc(node_factory):
     # The trailer is generated using the filler and can be ued as a
     # checksum. This trailer is from the test-vector in the specs.
     print(res)
-    assert(res['onion'].endswith('be89e4701eb870f8ed64fafa446c78df3ea'))
+    assert(res['onion'].endswith('9400f45a48e6dc8ddbaeb3'))
 
 
 @unittest.skipIf(not DEVELOPER, "gossip propagation is slow without DEVELOPER=1")