`TCP_USER_TIMEOUT` (since Linux 2.6.37) specifies the maximum amount of
time that transmitted data may remain unacknowledged before TCP will
forcibly close the connection and return `ETIMEDOUT` to the application.
Setting a low TCP user timeout allows RPC connections quickly reroute
around unavailable storage nodes during network interruptions.
Previously netstorage.MustStop() call didn't free up all the resources,
so the subsequent call to nestorage.Init() would panic.
This allows writing tests, which call nestorage.Init() + nestorage.MustStop() in a loop.
