rpc: set MaxGasInvoke in config

Implement ability to restrict maximum amount of GAS
available for free RPC calls.

config/config.go

@@ -96,6 +96,9 @@ type (
 		EnableCORSWorkaround bool   `yaml:"EnableCORSWorkaround"`
 		Address              string `yaml:"Address"`
 		Port                 uint16 `yaml:"Port"`
+		// MaxGasInvoke is a maximum amount of gas which
+		// can be spent during RPC call.
+		MaxGasInvoke util.Fixed8 `yaml:"MaxGasInvoke"`
 	}
 
 	// NetMode describes the mode the blockchain will operate on.

pkg/rpc/server.go

@@ -396,6 +396,7 @@ func (s *Server) invokescript(reqParams Params) (interface{}, error) {
 // result.
 func (s *Server) runScriptInVM(script []byte) *wrappers.InvokeResult {
 	vm, _ := s.chain.GetTestVM()
+	vm.SetGasLimit(s.config.MaxGasInvoke)
 	vm.LoadScript(script)
 	_ = vm.Run()
 	result := &wrappers.InvokeResult{