lnd: make closechannel send an instant empty update when no_wait set

We do things this way to keep behavior consistent across REST, gRPC
and CLI consistent. This was done to not alter the way we handle
Recv calls from the streams.

lnrpc/lightning.swagger.json

@@ -866,6 +866,13 @@
             "required": false,
             "type": "string",
             "format": "uint64"
+          },
+          {
+            "name": "no_wait",
+            "description": "If true, then the rpc call will not block while it awaits a closing txid.\nConsequently this RPC call will not return a closing txid if this value\nis set.",
+            "in": "query",
+            "required": false,
+            "type": "boolean"
           }
         ],
         "tags": [
@@ -4367,6 +4374,9 @@
         },
         "chan_close": {
           "$ref": "#/definitions/lnrpcChannelCloseUpdate"
+        },
+        "close_instant": {
+          "$ref": "#/definitions/lnrpcInstantUpdate"
         }
       }
     },
@@ -5236,6 +5246,9 @@
       ],
       "default": "INITIATOR_UNKNOWN"
     },
+    "lnrpcInstantUpdate": {
+      "type": "object"
+    },
     "lnrpcInterceptFeedback": {
       "type": "object",
       "properties": {