syncppp: Fix crashes.

The syncppp layer wants a mid-level netdev private pointer.

It was using netdev->priv but that only worked by accident,
and thus this scheme was broken when the device private
allocation strategy changed.

Add a proper mid-layer private pointer for uses like this,
update syncppp and all users, and remove the HDLC_PPP broken
tag from drivers/net/wan/Kconfig

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/wan/Kconfig b/drivers/net/wan/Kconfig
index 8005dd1..d5140ae 100644
--- a/drivers/net/wan/Kconfig
+++ b/drivers/net/wan/Kconfig
@@ -150,11 +150,9 @@
 
 config HDLC_PPP
 	tristate "Synchronous Point-to-Point Protocol (PPP) support"
-	depends on HDLC && BROKEN
+	depends on HDLC
 	help
 	  Generic HDLC driver supporting PPP over WAN connections.
-	  This module is currently broken and will cause a kernel panic
-	  when a device configured in PPP mode is activated.
 
 	  It will be replaced by new PPP implementation in Linux 2.6.26.