ndp: NewNonce generates a 6 byte nonce

Signed-off-by: Matt Layher <[email protected]>

option.go

@@ -760,9 +760,9 @@ type Nonce struct {
 
 // NewNonce creates a Nonce option with an opaque random value.
 func NewNonce() *Nonce {
-	// Minimum is 6 bytes but the final length of the message must be a multiple
-	// of 8 bytes, so we'll go with 14 for now and re-evaluate later.
-	const n = 14
+	// Minimum is 6 bytes, and this is also the only value that the Linux kernel
+	// recognizes as of kernel 5.17.
+	const n = 6
 	b := make([]byte, n)
 	_, _ = rand.Read(b)
 

option_test.go

@@ -961,11 +961,21 @@ func nonceTests() []optionSub {
 			},
 			ok: true,
 		},
+		{
+			name: "ok, larger length",
+			os:   []Option{&Nonce{b: make([]byte, 14)}},
+			bs: [][]byte{
+				{14, 2},
+				// Nonce.
+				ndptest.Zero(14),
+			},
+			ok: true,
+		},
 		{
 			name: "ok, random",
 			os:   []Option{nonce},
 			bs: [][]byte{
-				{14, 2},
+				{14, 1},
 				// Nonce.
 				nonce.b,
 			},