rlp: add support for "-" struct tag

rlp/decode_test.go

@@ -339,6 +339,12 @@ var (
 	)
 )
 
+type hasIgnoredField struct {
+	A uint
+	B uint `rlp:"-"`
+	C uint
+}
+
 var decodeTests = []decodeTest{
 	// booleans
 	{input: "01", ptr: new(bool), value: true},
@@ -490,6 +496,13 @@ var decodeTests = []decodeTest{
 		value: tailRaw{A: 1, Tail: []RawValue{}},
 	},
 
+	// struct tag "-"
+	{
+		input: "C20102",
+		ptr:   new(hasIgnoredField),
+		value: hasIgnoredField{A: 1, C: 2},
+	},
+
 	// RawValue
 	{input: "01", ptr: new(RawValue), value: RawValue(unhex("01"))},
 	{input: "82FFFF", ptr: new(RawValue), value: RawValue(unhex("82FFFF"))},