lnwire+channeldb: parse inbound fees

In this commit, the tlv extension of a channel update message is parsed.
If an inbound fee schedule is encountered, it is reported in the
graph rpc calls.

lnrpc/devrpc/dev.swagger.json

@@ -217,6 +217,14 @@
             "format": "byte"
           },
           "description": "Custom channel update tlv records."
+        },
+        "inbound_fee_base_msat": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "inbound_fee_rate_milli_msat": {
+          "type": "integer",
+          "format": "int32"
         }
       }
     },

lnrpc/lightning.proto

@@ -3330,6 +3330,9 @@ message RoutingPolicy {
 
     // Custom channel update tlv records.
     map<uint64, bytes> custom_records = 8;
+
+    int32 inbound_fee_base_msat = 9;
+    int32 inbound_fee_rate_milli_msat = 10;
 }
 
 /*

lnrpc/lightning.swagger.json

@@ -6840,6 +6840,14 @@
             "format": "byte"
           },
           "description": "Custom channel update tlv records."
+        },
+        "inbound_fee_base_msat": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "inbound_fee_rate_milli_msat": {
+          "type": "integer",
+          "format": "int32"
         }
       }
     },