IPSec NMI initialization and termination messages

When a client successfully connects to the interface, the server sends an initialization message (a message with type NMsec_INIT) to the client. This message contains no records, but the return code and reason code are 0 to indicate successful connection completion. When the server closes the connection (this might be the result of error, IKED termination, or the client's closing of the socket), the server attempts to send a termination message (a message with type NMsec_TERM) to the client. This message contains no records, but the return code and reason code indicate the cause of the connection's termination.