sphinx: Passing shared secret of the HTLC up to the master

This is needed so we can create error messages and wrap them on the
way back.

lightningd/channel/channel.c

@@ -651,7 +651,8 @@ static void their_htlc_locked(const struct htlc *htlc, struct peer *peer)
 					   rs->nextcase == ONION_FORWARD,
 					   rs->hop_data.amt_forward,
 					   rs->hop_data.outgoing_cltv,
-					   &rs->hop_data.channel_id);
+					   &rs->hop_data.channel_id,
+					   &ss);
 	daemon_conn_send(&peer->master, take(msg));
 	tal_free(tmpctx);
 	return;

lightningd/channel/channel_wire.csv

@@ -88,6 +88,7 @@ channel_accepted_htlc,0,forward,bool
 channel_accepted_htlc,0,amt_to_forward,u64
 channel_accepted_htlc,0,outgoing_cltv_value,u32
 channel_accepted_htlc,0,next_channel,struct short_channel_id
+channel_accepted_htlc,0,shared_secret,32
 
 # FIXME: Add code to commit current channel state!
 

lightningd/htlc_end.h

@@ -28,6 +28,7 @@ struct htlc_end {
 	u32 outgoing_cltv_value;
 	u32 cltv_expiry;
 	struct sha256 payment_hash;
+	struct sha256 shared_secret;
 };
 
 static inline const struct htlc_end *keyof_htlc_end(const struct htlc_end *e)

lightningd/peer_control.c

@@ -1088,7 +1088,8 @@ static int peer_accepted_htlc(struct peer *peer, const u8 *msg)
 					    hend->next_onion, &forward,
 					    &hend->amt_to_forward,
 					    &hend->outgoing_cltv_value,
-					    &hend->next_channel)) {
+					    &hend->next_channel,
+					    &hend->shared_secret)) {
 		log_broken(peer->log, "bad fromwire_channel_accepted_htlc %s",
 			   tal_hex(peer, msg));
 		return -1;