AZL-68769

In the Linux kernel, the following vulnerability has been resolved:

ipvs: Defer ipvsftp unregister during netns cleanup

On the netns cleanup path, _ipvsftpexit() may unregister ipvsftp before connections with valid cp->app pointers are flushed, leading to a use-after-free.

Fix this by introducing a global exiting_module flag, set to true in ipvsftp_exit() before unregistering the pernet subsystem. In __ipvsftpexit(), skip ipvsftp unregister if called during netns cleanup (when exitingmodule is false) and defer it to _ipvscleanupbatch(), which unregisters all apps after all connections are flushed. If called during module exit, unregister ipvsftp immediately.