SpeedTouch USB workaround

[Diego]

Hi people,

SpeedTouch stop working since last year (if I remember correctly, around 
April - May).
http://www.freebsd.org/cgi/query-pr.cgi?pr=usb/83504
BTW I found a workaround that works in RELENG_6 and HEAD (I tested it in 
HEAD
but I think it will work on RELENG_6).

I suppose that threads of modem_run occupy the usb device. After 
modem_run, kill it!
And then you can call  ppp -background your_profile  without crash ;-)

Summary:

modem_run -f mgmt.o
---> killall modem_run <---
ppp -background -nat your_profile

For unbreak pppoa in HEAD substitute this:

+	*-freebsd[56]*)

with

+	*-freebsd[567]*)

and remove from Makefile:

.if ${OSVERSION} >= 700000

BROKEN=			"Does not build on FreeBSD >= 7.0"
.endif