reflect: correct Type.FieldByNameFunc docs

Fixes #16573.

Change-Id: I5a26eaa8b258cb1861190f9690086725532b8a0d
Reviewed-on: https://go-review.googlesource.com/31354Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/reflect/type.go

@@ -156,9 +156,14 @@ type Type interface {
 	// and a boolean indicating if the field was found.
 	FieldByName(name string) (StructField, bool)
 
-	// FieldByNameFunc returns the first struct field with a name
+	// FieldByNameFunc returns the struct field with a name
 	// that satisfies the match function and a boolean indicating if
 	// the field was found.
+	//
+	// If multiple fields match the func, they cancel each other
+	// and FieldByNameFunc returns no match.
+	// This behavior mirrors Go's handling of name lookup in
+	// structs containing anonymous fields.
 	FieldByNameFunc(match func(string) bool) (StructField, bool)
 
 	// In returns the type of a function type's i'th input parameter.