Update mockgen.go

Author: klaidliadon

mockgen/mockgen.go

@@ -782,15 +782,15 @@ func (g *generator) getArgNames(m *model.Method, in bool) []string {
 		name := p.Name
 
 		if name == "" || name == "_" || g.nameExistsAsPackage(name) {
-			name = fmt.Sprintf("arg%d", i)
+			name = "_" + name
 		}
 		argNames[i] = name
 	}
 	if m.Variadic != nil && in {
 		name := m.Variadic.Name
 
 		if name == "" || g.nameExistsAsPackage(name) {
-			name = fmt.Sprintf("arg%d", len(params))
+			name = name = "_" + name
 		}
 		argNames = append(argNames, name)
 	}