[L2TP]: PPP over L2TP driver core

This driver handles only L2TP data frames; control frames are handled
by a userspace application. It implements L2TP using the PPPoX socket
family. There is a PPPoX socket for each L2TP session in an L2TP
tunnel.  PPP data within each session is passed through the kernel's
PPP subsystem via this driver. Kernel parameters of each socket can be
read or modified using ioctl() or [gs]etsockopt() calls.
Signed-off-by: NJames Chapman <jchapman@katalix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -2784,6 +2784,19 @@ config PPPOATM
 	  which can lead to bad results if the ATM peer loses state and
 	  changes its encapsulation unilaterally.
 
+config PPPOL2TP
+	tristate "PPP over L2TP (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && PPP
+	help
+	  Support for PPP-over-L2TP socket family. L2TP is a protocol
+	  used by ISPs and enterprises to tunnel PPP traffic over UDP
+	  tunnels. L2TP is replacing PPTP for VPN uses.
+
+	  This kernel component handles only L2TP data packets: a
+	  userland daemon handles L2TP the control protocol (tunnel
+	  and session setup). One such daemon is OpenL2TP
+	  (http://openl2tp.sourceforge.net/).
+
 config SLIP
 	tristate "SLIP (serial line) support"
 	---help---

drivers/net/Makefile

@@ -121,6 +121,7 @@ obj-$(CONFIG_PPP_DEFLATE) += ppp_deflate.o
 obj-$(CONFIG_PPP_BSDCOMP) += bsd_comp.o
 obj-$(CONFIG_PPP_MPPE) += ppp_mppe.o
 obj-$(CONFIG_PPPOE) += pppox.o pppoe.o
+obj-$(CONFIG_PPPOL2TP) += pppox.o pppol2tp.o
 
 obj-$(CONFIG_SLIP) += slip.o
 obj-$(CONFIG_SLHC) += slhc.o