cli: Add warning for duplicate port definition

Adds a warning when both -rpcconnect and -rpcport define
a port to be used.

src/bitcoin-cli.cpp

@@ -768,6 +768,12 @@ static UniValue CallRPC(BaseRequestHandler* rh, const std::string& strMethod, co
 
             // Use the valid port provided
             port = rpcport_port.value();
+
+            // If there was a valid port provided in rpcconnect,
+            // rpcconnect_port is non-zero.
+            if (rpcconnect_port != 0) {
+                tfm::format(std::cerr, "Warning: Port specified in both -rpcconnect and -rpcport. Using -rpcport %u\n", port);
+            }
         }
     }