[pptp-server] PPTP with PPP in sync mode problem

[Sang Yu]

Dear James Cameron,

I think that the sync patch is unstable currently because it is frequently
disconnected whenever data transfering with the following errors from
pptp server.

-pptpd[2246]: GRE: read (fd=5,buffer=804d8c0,len=8196) from PTY failed:
status = - 1 errror = Input/output error
-pptpd[2246]: CTRL: PTY read or GRE write failed (pty,gre)=(5,6)
-pptpd[2246]: CTRL: Client 192.168.1.12 control connection finished

* and the "slow" means that if upload performance is 8~9Mbps on 10Mbps
   ethernet, download is 50~70Kbps.

Many thanks,
Sang