Do not search inherited methods for parameter attributes

It looks like .NET Framework, .NET Core, and previous versions of Mono
agree that GetCustomAttributes should not search base class methods
looking for attributes on parameters.

Author: Josh Peterson

mcs/class/corlib/System/MonoCustomAttrs.cs

@@ -183,6 +183,9 @@ internal static object[] GetCustomAttributes (ICustomAttributeProvider obj, Type
 			if (inherit && GetBase (obj) == null)
 				inherit = false;
 
+			if (obj is RuntimeParameterInfo)
+				inherit = false;
+
 			// if AttributeType is sealed, and Inherited is set to false, then 
 			// there's no use in scanning base types 
 			if ((attributeType != null && attributeType.IsSealed) && inherit) {