[core] Fixed group synchronization of accepted sockets.

Fixes #2941.

srtcore/core.cpp

@@ -5800,6 +5800,16 @@ void srt::CUDT::acceptAndRespond(const sockaddr_any& agent, const sockaddr_any&
         throw CUDTException(MJ_SETUP, MN_REJECTED, 0);
     }
 
+#if ENABLE_BONDING
+    // The socket and the group are only linked to each other after interpretSrtHandshake(..) has been called.
+    // Keep the group alive for the lifetime of this function,
+    // and do it BEFORE acquiring m_ConnectionLock to avoid
+    // lock inversion.
+    // This will check if a socket belongs to a group and if so
+    // it will remember this group and keep it alive here.
+    CUDTUnited::GroupKeeper group_keeper(uglobal(), m_parent);
+#endif
+
     if (!prepareBuffers(NULL))
     {
         HLOGC(cnlog.Debug,