lnrpc: add remote_max_htlcs to OpenChannelRequest

This will allow users to set a custom limit for the max number of
concurrent HTLCs the remote party can add to the channel.

lnrpc/rpc.proto

@@ -1685,6 +1685,12 @@ message OpenChannelRequest {
     the channel. It only applies to the remote party.
     */
     uint64 remote_max_value_in_flight_msat = 15;
+
+    /*
+    The maximum number of concurrent HTLCs we will allow the remote party to add
+    to the commitment transaction.
+    */
+    uint32 remote_max_htlcs = 16;
 }
 message OpenStatusUpdate {
     oneof update {

lnrpc/rpc.swagger.json

@@ -4494,6 +4494,11 @@
           "type": "string",
           "format": "uint64",
           "description": "The maximum amount of coins in millisatoshi that can be pending within\nthe channel. It only applies to the remote party."
+        },
+        "remote_max_htlcs": {
+          "type": "integer",
+          "format": "int64",
+          "description": "The maximum number of concurrent HTLCs we will allow the remote party to add\nto the commitment transaction."
         }
       }
     },