pfcp: add PFCP module

Packet Forwarding Control Protocol (PFCP) is a 3GPP Protocol
used between the control plane and the user plane function.
It is specified in TS 29.244[1].

Note that this module is not designed to support this Protocol
in the kernel space. There is no support for parsing any PFCP messages.
There is no API that could be used by any userspace daemon.
Basically it does not support PFCP. This protocol is sophisticated
and there is no need for implementing it in the kernel. The purpose
of this module is to allow users to setup software and hardware offload
of PFCP packets using tc tool.

When user requests to create a PFCP device, a new socket is created.
The socket is set up with port number 8805 which is specific for
PFCP [29.244 4.2.2]. This allow to receive PFCP request messages,
response messages use other ports.

Note that only one PFCP netdev can be created.

Only IPv4 is supported at this time.

[1] https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=3111

Signed-off-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Marcin Szycik <marcin.szycik@linux.intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -290,6 +290,19 @@ config GTP
 	  To compile this drivers as a module, choose M here: the module
 	  will be called gtp.
 
+config PFCP
+	tristate "Packet Forwarding Control Protocol (PFCP)"
+	depends on INET
+	select NET_UDP_TUNNEL
+	help
+	  This allows one to create PFCP virtual interfaces that allows to
+	  set up software and hardware offload of PFCP packets.
+	  Note that this module does not support PFCP protocol in the kernel space.
+	  There is no support for parsing any PFCP messages.
+
+	  To compile this drivers as a module, choose M here: the module
+	  will be called pfcp.
+
 config AMT
 	tristate "Automatic Multicast Tunneling (AMT)"
 	depends on INET && IP_MULTICAST