Workaround for project-chip#12821, session ID collissions

Add a central session ID allocator in mSystemState so aware consumers
can avoid collision.

src/transport/SessionManager.h

@@ -33,6 +33,7 @@
 #include <lib/support/DLLUtil.h>
 #include <messaging/ReliableMessageProtocolConfig.h>
 #include <protocols/secure_channel/Constants.h>
+#include <protocols/secure_channel/SessionIDAllocator.h>
 #include <transport/CryptoContext.h>
 #include <transport/MessageCounterManagerInterface.h>
 #include <transport/SecureSessionTable.h>
@@ -247,6 +248,12 @@ class DLL_EXPORT SessionManager : public TransportMgrDelegate
     // and tv-casting-app that uses the TV's node ID to find the associated secure session
     SessionHandle FindSecureSessionForNode(NodeId peerNodeId);
 
+    /**
+     * @brief
+     *  Return the session ID allocator for this session manager instance.
+     */
+    SessionIDAllocator * GetSessionIDAllocator() { return &mIDAllocator; }
+
 private:
     /**
      *    The State of a secure transport object.
@@ -263,6 +270,8 @@ class DLL_EXPORT SessionManager : public TransportMgrDelegate
         kPayloadIsUnencrypted,
     };
 
+    SessionIDAllocator mIDAllocator;
+
     System::Layer * mSystemLayer = nullptr;
     Transport::UnauthenticatedSessionTable<CHIP_CONFIG_UNAUTHENTICATED_CONNECTION_POOL_SIZE> mUnauthenticatedSessions;
     Transport::SecureSessionTable<CHIP_CONFIG_PEER_CONNECTION_POOL_SIZE> mSecureSessions; // < Active connections to other peers