Several problems that can lead to bugs/memory leaks

[EvgeniiMekhanik]

1. When we use tfw_sock_srv_grace_shutdown_sg we call tfw_sock_srv_grace_shutdown_srv, where we try to
   disconnect servers or add server to special list for further disconnection. For all such servers we never call tfw_sock_srv_abort_srv. So if disconnect fail we catch bug or memory leak during Tempesta FW unloading.
2. We iterate over all servers using tfw_sg_for_each_srv. If one of the tfw_sock_srv_disconnect_srv failed we never call it for other servers.
3. In case of problems with memory allocations connection abortion can fail, that lead to bugs/memory leaks