[PATCH] Generic HDLC WAN drivers - disable netif_carrier_off()

As we are currently unable to fix the problem with carrier and protocol
state signaling in net core I've to disable netif_carrier_off()
calls used by WAN protocol drivers. The attached patch should make
them working again.

The remaining netif_carrier_*() calls in hdlc_fr.c are fine as they
don't touch the physical device.

Signed-off-by: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: John W. Linville <linville@tuxdriver.com>