Mark generic HDLC + PPP as broken.

PPP support in generic HDLC in Linux 2.6.25 is broken and will cause
a kernel panic when a device configured in PPP mode is activated.

It will be replaced by new PPP implementation after Linux 2.6.25 is
released.

This affects only PPP support in generic HDLC (mostly Hitachi SCA
and SCA-II based drivers, wanxl, and few others). Standalone syncppp
and async PPP support are not affected.

Signed-off-by: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>