Assert UpdatedAtNanos in neighbor cache tests

Changes the neighbor_cache_test.go tests to always assert UpdatedAtNanos.

Completes the assertion of UpdatedAtNanos in every NUD test, a field that was
historically not checked due to the lack of a deterministic, controllable
clock. This is no longer true with the tcpip.Clock interface. While the tests
have been adjusted to use Clock, asserting by the UpdatedAtNanos was neglected.

Fixes #4663

PiperOrigin-RevId: 360730077

pkg/tcpip/stack/neighbor_entry_test.go

@@ -18,13 +18,11 @@ import (
 	"fmt"
 	"math"
 	"math/rand"
-	"strings"
 	"sync"
 	"testing"
 	"time"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/google/go-cmp/cmp/cmpopts"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/faketime"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
@@ -52,23 +50,6 @@ func runImmediatelyScheduledJobs(clock *faketime.ManualClock) {
 	clock.Advance(immediateDuration)
 }
 
-// eventDiffOpts are the options passed to cmp.Diff to compare entry events.
-// The UpdatedAtNanos field is ignored due to a lack of a deterministic method
-// to predict the time that an event will be dispatched.
-func eventDiffOpts() []cmp.Option {
-	return []cmp.Option{
-		cmpopts.IgnoreFields(NeighborEntry{}, "UpdatedAtNanos"),
-	}
-}
-
-// eventDiffOptsWithSort is like eventDiffOpts but also includes an option to
-// sort slices of events for cases where ordering must be ignored.
-func eventDiffOptsWithSort() []cmp.Option {
-	return append(eventDiffOpts(), cmpopts.SortSlices(func(a, b testEntryEventInfo) bool {
-		return strings.Compare(string(a.Entry.Addr), string(b.Entry.Addr)) < 0
-	}))
-}
-
 // The following unit tests exercise every state transition and verify its
 // behavior with RFC 4681 and RFC 7048.
 //