Fix CASEServer cleanup to not nuke unrelated CASE handshakes.

We could run into a problem when an invalid Sigma1 (e.g. not matching any
fabric) was received, because we would do the following:

1) Call CASEServer::OnSessionEstablishmentError from inside
   CASESession::OnMessageReceived, which would queue a task to blow away the
   CASEServer state and start listening for new CASE handshakes
   (PrepareForSessionEstablishment).

2) Return an error from CASESession::OnMessageReceived, which would cause us to
   synchronously do call PrepareForSessionEstablishment.

If we now got a new Sigma1 before the async task ran (e.g. if it was already
waiting in the queue), we could respond to the Sigma1 with Sigma2Resume, then
the async task would run and blow away our state.

We would end up in a situation where the other side then sends a StatusResponse
and thinks CASE is established, but on our end we don't recognize the session ID
for the session they think has been established.

The fix is to restrict the async behavior to the one case it's actually needed
(OnSessionReleased), for both CASE and PASE, to synchronously call
PrepareForSessionEstablishment from OnSessionEstablishmentError, and to remove
the now-redundant PrepareForSessionEstablishment call on error return from
CASESession::OnMessageReceived.

src/protocols/secure_channel/CASEServer.cpp

@@ -86,11 +86,8 @@ CHIP_ERROR CASEServer::OnMessageReceived(Messaging::ExchangeContext * ec, const
     SuccessOrExit(err);
 
 exit:
-    if (err != CHIP_NO_ERROR)
-    {
-        PrepareForSessionEstablishment();
-    }
-
+    // CASESession::OnMessageReceived guarantees that it will call
+    // OnSessionEstablishmentError if it returns error, so nothing else to do here.
     return err;
 }
 
@@ -157,16 +154,7 @@ void CASEServer::OnSessionEstablishmentError(CHIP_ERROR err)
 {
     ChipLogError(Inet, "CASE Session establishment failed: %" CHIP_ERROR_FORMAT, err.Format());
 
-    //
-    // We're not allowed to call methods that will eventually result in calling SessionManager::AllocateSecureSession
-    // from a SessionDelegate::OnSessionReleased callback. Schedule the preparation as an async work item.
-    //
-    mSessionManager->SystemLayer()->ScheduleWork(
-        [](auto * systemLayer, auto * appState) -> void {
-            CASEServer * _this = static_cast<CASEServer *>(appState);
-            _this->PrepareForSessionEstablishment();
-        },
-        this);
+    PrepareForSessionEstablishment();
 }
 
 void CASEServer::OnSessionEstablished(const SessionHandle & session)

src/protocols/secure_channel/CASESession.cpp

@@ -134,9 +134,9 @@ CASESession::~CASESession()
 
 void CASESession::OnSessionReleased()
 {
+    // Call into our super-class before we clear our state.
+    PairingSession::OnSessionReleased();
     Clear();
-    // Do this last in case the delegate frees us.
-    NotifySessionEstablishmentError(CHIP_ERROR_CONNECTION_ABORTED);
 }
 
 void CASESession::Clear()

src/protocols/secure_channel/PASESession.cpp

@@ -75,9 +75,9 @@ PASESession::~PASESession()
 
 void PASESession::OnSessionReleased()
 {
+    // Call into our super-class before we clear our state.
+    PairingSession::OnSessionReleased();
     Clear();
-    // Do this last in case the delegate frees us.
-    NotifySessionEstablishmentError(CHIP_ERROR_CONNECTION_ABORTED);
 }
 
 void PASESession::Finish()

src/protocols/secure_channel/PairingSession.cpp

@@ -182,4 +182,23 @@ void PairingSession::NotifySessionEstablishmentError(CHIP_ERROR error)
     delegate->OnSessionEstablishmentError(error);
 }
 
+void PairingSession::OnSessionReleased()
+{
+    // Send the error notification async, because our delegate is likely to want
+    // to create a new session to listen for new connection attempts, and doing
+    // that under an OnSessionReleased notification is not safe.
+    if (!mSessionManager)
+    {
+        return;
+    }
+
+    mSessionManager->SystemLayer()->ScheduleWork(
+        [](auto * systemLayer, auto * appState) -> void {
+            ChipLogError(Inet, "ASYNC CASE Session establishment failed");
+            auto * _this = static_cast<PairingSession *>(appState);
+            _this->NotifySessionEstablishmentError(CHIP_ERROR_CONNECTION_ABORTED);
+        },
+        this);
+}
+
 } // namespace chip

src/protocols/secure_channel/PairingSession.h

@@ -51,6 +51,7 @@ class DLL_EXPORT PairingSession : public SessionDelegate
 
     // Implement SessionDelegate
     NewSessionHandlingPolicy GetNewSessionHandlingPolicy() override { return NewSessionHandlingPolicy::kStayAtOldSession; }
+    void OnSessionReleased() override;
 
     Optional<uint16_t> GetLocalSessionId() const
     {