p2p, swarm: fix node up races by granular locking (#18976)

* swarm/network: DRY out repeated giga comment

I not necessarily agree with the way we wait for event propagation.
But I truly disagree with having duplicated giga comments.

* p2p/simulations: encapsulate Node.Up field so we avoid data races

The Node.Up field was accessed concurrently without "proper" locking.
There was a lock on Network and that was used sometimes to access
the  field. Other times the locking was missed and we had
a data race.

For example: https://github.com/ethereum/go-ethereum/pull/18464
The case above was solved, but there were still intermittent/hard to
reproduce races. So let's solve the issue permanently.

resolves: ethersphere/go-ethereum#1146

* p2p/simulations: fix unmarshal of simulations.Node

Making Node.Up field private in 13292ee897
broke TestHTTPNetwork and TestHTTPSnapshot. Because the default
UnmarshalJSON does not handle unexported fields.

Important: The fix is partial and not proper to my taste. But I cut
scope as I think the fix may require a change to the current
serialization format. New ticket:
https://github.com/ethersphere/go-ethereum/issues/1177

* p2p/simulations: Add a sanity test case for Node.Config UnmarshalJSON

* p2p/simulations: revert back to defer Unlock() pattern for Network

It's a good patten to call `defer Unlock()` right after `Lock()` so
(new) error cases won't miss to unlock. Let's get back to that pattern.

The patten was abandoned in 85a79b3ad3,
while fixing a data race. That data race does not exist anymore,
since the Node.Up field got hidden behind its own lock.

* p2p/simulations: consistent naming for test providers Node.UnmarshalJSON

* p2p/simulations: remove JSON annotation from private fields of Node

As unexported fields are not serialized.

* p2p/simulations: fix deadlock in Network.GetRandomDownNode()

Problem: GetRandomDownNode() locks -> getDownNodeIDs() ->
GetNodes() tries to lock -> deadlock

On Network type, unexported functions must assume that `net.lock`
is already acquired and should not call exported functions which
might try to lock again.

* p2p/simulations: ensure method conformity for Network

Connect* methods were moved to p2p/simulations.Network from
swarm/network/simulation. However these new methods did not follow
the pattern of Network methods, i.e., all exported method locks
the whole Network either for read or write.

* p2p/simulations: fix deadlock during network shutdown

`TestDiscoveryPersistenceSimulationSimAdapter` often got into deadlock.
The execution was stuck on two locks, i.e, `Kademlia.lock` and
`p2p/simulations.Network.lock`. Usually the test got stuck once in each
20 executions with high confidence.

`Kademlia` was stuck in `Kademlia.EachAddr()` and `Network` in
`Network.Stop()`.

Solution: in `Network.Stop()` `net.lock` must be released before
calling `node.Stop()` as stopping a node (somehow - I did not find
the exact code path) causes `Network.InitConn()` to be called from
`Kademlia.SuggestPeer()` and that blocks on `net.lock`.

Related ticket: https://github.com/ethersphere/go-ethereum/issues/1223

* swarm/state: simplify if statement in DBStore.Put()

* p2p/simulations: remove faulty godoc from private function

The comment started with the wrong method name.

The method is simple and self explanatory. Also, it's private.
=> Let's just remove the comment.

p2p/simulations/http_test.go

@@ -421,14 +421,15 @@ type expectEvents struct {
 }
 
 func (t *expectEvents) nodeEvent(id string, up bool) *Event {
+	node := Node{
+		Config: &adapters.NodeConfig{
+			ID: enode.HexID(id),
+		},
+		up: up,
+	}
 	return &Event{
 		Type: EventTypeNode,
-		Node: &Node{
-			Config: &adapters.NodeConfig{
-				ID: enode.HexID(id),
-			},
-			Up: up,
-		},
+		Node: &node,
 	}
 }
 
@@ -480,6 +481,7 @@ loop:
 }
 
 func (t *expectEvents) expect(events ...*Event) {
+	t.Helper()
 	timeout := time.After(10 * time.Second)
 	i := 0
 	for {
@@ -501,8 +503,8 @@ func (t *expectEvents) expect(events ...*Event) {
 				if event.Node.ID() != expected.Node.ID() {
 					t.Fatalf("expected node event %d to have id %q, got %q", i, expected.Node.ID().TerminalString(), event.Node.ID().TerminalString())
 				}
-				if event.Node.Up != expected.Node.Up {
-					t.Fatalf("expected node event %d to have up=%t, got up=%t", i, expected.Node.Up, event.Node.Up)
+				if event.Node.Up() != expected.Node.Up() {
+					t.Fatalf("expected node event %d to have up=%t, got up=%t", i, expected.Node.Up(), event.Node.Up())
 				}
 
 			case EventTypeConn: