Suspend accepting new client connections.
A value of zero is returned if the server has suspended accepting
otherwise a non-zero error code is returned which indicates the cause
of the failure.
The Suspend method instructs the server to suspend
accepting new client connections. All new clients that attempt to
connect to the server will be sent a 421 "service unavailable" error
code and the connection will be immediately closed. To resume accepting
new client connections, call the
Resume method. This method will not affect those clients that
have already established a connection with the server before the
Suspend method was called.