Fix a bug where sc_ctlp() is improperly called when the packet is passed up

Fix a bug where sc_ctlp() is improperly called when the packet is passed up
the protocol stack.  sc_ctlp() must be called exactly once for each packet
queued to the tty and ONLY when the packet is queued to the tty.  Otherwise
the tty's t_canq will start to fill up and the tty code will incorrectly
believe that there are packets pending when there might not be.

The characteristic of this bug was that pppd would stay in a 'R'un state
polling the tty for non-existant packets.

Reported-by: =?ISO-8859-1?Q?Cristi=E1n_H=2E_Garc=EDa_Whiting?= <cgw@cosimo.cl>,
		Sarunas Vancevicius <vsarunas@eircom.net>