Remove deprecated NUD types Failed and FailedEntryLookups

Completes the soft migration to Unreachable state by removing the Failed state
and the the FailedEntryLookups StatCounter.

Fixes #4667

PiperOrigin-RevId: 358226380

pkg/tcpip/stack/neighbor_cache.go

@@ -25,10 +25,6 @@ const neighborCacheSize = 512 // max entries per interface
 
 // NeighborStats holds metrics for the neighbor table.
 type NeighborStats struct {
-	// FailedEntryLookups is deprecated; UnreachableEntryLookups should be used
-	// instead.
-	FailedEntryLookups *tcpip.StatCounter
-
 	// UnreachableEntryLookups counts the number of lookups performed on an
 	// entry in Unreachable state.
 	UnreachableEntryLookups *tcpip.StatCounter

pkg/tcpip/stack/neighbor_entry.go

@@ -68,11 +68,6 @@ const (
 	// Static describes entries that have been explicitly added by the user. They
 	// do not expire and are not deleted until explicitly removed.
 	Static
-	// Failed is deprecated and should no longer be used.
-	//
-	// TODO(gvisor.dev/issue/4667): Remove this once all references to Failed
-	// are removed from Fuchsia.
-	Failed
 	// Unreachable means reachability confirmation failed; the maximum number of
 	// reachability probes has been sent and no replies have been received.
 	//

pkg/tcpip/stack/neighborstate_string.go

@@ -29,13 +29,12 @@ func _() {
 	_ = x[Delay-4]
 	_ = x[Probe-5]
 	_ = x[Static-6]
-	_ = x[Failed-7]
-	_ = x[Unreachable-8]
+	_ = x[Unreachable-7]
 }
 
-const _NeighborState_name = "UnknownIncompleteReachableStaleDelayProbeStaticFailedUnreachable"
+const _NeighborState_name = "UnknownIncompleteReachableStaleDelayProbeStaticUnreachable"
 
-var _NeighborState_index = [...]uint8{0, 7, 17, 26, 31, 36, 41, 47, 53, 64}
+var _NeighborState_index = [...]uint8{0, 7, 17, 26, 31, 36, 41, 47, 58}
 
 func (i NeighborState) String() string {
 	if i >= NeighborState(len(_NeighborState_index)-1) {