lightningd: add "style" to listforwards.

Suggested-by: @t-bast
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Added: JSON-RPC: `listforwards` has new entry `style`, currently "legacy" or "tlv".

doc/lightning-listforwards.7.md

@@ -29,6 +29,7 @@ On success, an object containing **forwards** is returned.  It is an array of ob
 - **received_time** (number): the UNIX timestamp when this was received
 - **out_channel** (short_channel_id, optional): the channel that the HTLC was forwarded to
 - **payment_hash** (hex, optional): payment hash sought by HTLC (always 64 characters)
+- **style** (string, optional): Either a legacy onion format or a modern tlv format (one of "legacy", "tlv")
 
 If **out_channel** is present:
   - **fee_msat** (msat): the amount this paid in fees
@@ -58,4 +59,4 @@ RESOURCES
 
 Main web site: <https://github.com/ElementsProject/lightning>
 
-[comment]: # ( SHA256STAMP:abfaaa00817734d8acb77d02d7c024112c90605a8f93a134971a617ab4d383f9)
+[comment]: # ( SHA256STAMP:131410f052b8a1845c8d3c7eb2d48df0fc7638e7d26817f56863815be86d8f1e)

doc/schemas/listforwards.schema.json

@@ -52,6 +52,14 @@
             "description": "payment hash sought by HTLC",
             "maxLength": 64,
             "minLength": 64
+          },
+          "style": {
+            "type": "string",
+            "enum": [
+              "legacy",
+              "tlv"
+            ],
+            "description": "Either a legacy onion format or a modern tlv format"
           }
         },
         "allOf": [
@@ -72,6 +80,7 @@
                 "in_msatoshi": {},
                 "in_msat": {},
                 "status": {},
+                "style": {},
                 "received_time": {},
                 "resolved_time": {},
                 "out_channel": {},
@@ -102,6 +111,7 @@
                 "in_msatoshi": {},
                 "in_msat": {},
                 "status": {},
+                "style": {},
                 "received_time": {},
                 "resolved_time": {},
                 "payment_hash": {},
@@ -132,6 +142,7 @@
                 "in_msatoshi": {},
                 "in_msat": {},
                 "status": {},
+                "style": {},
                 "received_time": {},
                 "out_channel": {},
                 "payment_hash": {},
@@ -154,6 +165,7 @@
                 "in_msatoshi": {},
                 "in_msat": {},
                 "status": {},
+                "style": {},
                 "received_time": {},
                 "out_channel": {},
                 "payment_hash": {},
@@ -186,6 +198,7 @@
                 "in_msatoshi": {},
                 "in_msat": {},
                 "status": {},
+                "style": {},
                 "received_time": {},
                 "out_channel": {},
                 "payment_hash": {},
@@ -212,6 +225,7 @@
                 "in_msatoshi": {},
                 "in_msat": {},
                 "status": {},
+                "style": {},
                 "received_time": {},
                 "out_channel": {},
                 "payment_hash": {},