This function waits until the PPP connection is running and then
returns. This is needed because the actual bring up of the connection
happens mostly after the call to cyg_ppp_up()
returns, and may take some time to complete, especially if dialling a
remote server.
The result of this call will be zero when the connection is running,
or -1 if the connection failed to start for some reason. If the
connection is already running when this call is made it will return
immediately with a zero result. If the connection is not in the
process of coming up, or has failed, or has terminated, then a result
of -1 will be returned immediately. Thus this function may also be
used to test that the connection is still running at any point.
