Remove the MonotonicTime.Nanoseconds() accessor.

Updates #7338.

PiperOrigin-RevId: 448360987

pkg/tcpip/network/internal/multicast/example_test.go

@@ -103,7 +103,7 @@ func Example() {
 		panic(fmt.Sprintf("table.GetLastUsedTimestamp(%#v) = (_, false)", routeKey))
 	}
 
-	fmt.Printf("Last used timestamp: %d", timestamp.Nanoseconds())
+	fmt.Printf("Last used timestamp: %s", timestamp)
 
 	// Finally, to remove an installed route, call:
 	if removed := table.RemoveInstalledRoute(routeKey); !removed {

pkg/tcpip/network/internal/multicast/route_table_test.go

@@ -452,8 +452,8 @@ func TestSetLastUsedTimestamp(t *testing.T) {
 				t.Fatalf("got table.GetLastUsedTimestamp(%#v) = (_, false_), want = (_, true)", defaultRouteKey)
 			}
 
-			if got, want := timestamp.Nanoseconds(), test.wantLastUsedTime.Nanoseconds(); got != want {
-				t.Errorf("got table.GetLastUsedTimestamp(%#v) = (%v, _), want (%v, _)", defaultRouteKey, got, want)
+			if timestamp != test.wantLastUsedTime {
+				t.Errorf("got table.GetLastUsedTimestamp(%#v) = (%s, _), want = (%s, _)", defaultRouteKey, timestamp, test.wantLastUsedTime)
 			}
 		})
 	}

pkg/tcpip/tcpip.go

@@ -71,9 +71,9 @@ type MonotonicTime struct {
 	nanoseconds int64
 }
 
-// Nanoseconds returns the monotonic time in nanoseconds.
-func (mt MonotonicTime) Nanoseconds() int64 {
-	return mt.nanoseconds
+// String implements Stringer.
+func (mt MonotonicTime) String() string {
+	return strconv.FormatInt(mt.nanoseconds, 10)
 }
 
 // Before reports whether the monotonic clock reading mt is before u.