lwtunnel: infrastructure for handling light weight tunnels like mpls

Provides infrastructure to parse/dump/store encap information for
light weight tunnels like mpls. Encap information for such tunnels
is associated with fib routes.

This infrastructure is based on previous suggestions from
Eric Biederman to follow the xfrm infrastructure.

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/Kconfig b/net/Kconfig
index 57a7c5a..7021c1b 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -374,6 +374,13 @@
 source "net/ceph/Kconfig"
 source "net/nfc/Kconfig"
 
+config LWTUNNEL
+	bool "Network light weight tunnels"
+	---help---
+	  This feature provides an infrastructure to support light weight
+	  tunnels like mpls. There is no netdevice associated with a light
+	  weight tunnel endpoint. Tunnel encapsulation parameters are stored
+	  with light weight tunnel state associated with fib routes.
 
 endif   # if NET