netdevsim: add software driver for testing offloads

To be able to run selftests without any hardware required we
need a software model.  The model can also serve as an example
implementation for those implementing actual HW offloads.
The dummy driver have previously been extended to test SR-IOV,
but the general consensus seems to be against adding further
features to it.

Add a new driver for purposes of software modelling only.
eBPF and SR-IOV will be added here shortly, others are invited
to further extend the driver with their offload models.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 0936da5..944ec3c 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -497,4 +497,15 @@
 
 source "drivers/net/hyperv/Kconfig"
 
+config NETDEVSIM
+	tristate "Simulated networking device"
+	depends on DEBUG_FS
+	help
+	  This driver is a developer testing tool and software model that can
+	  be used to test various control path networking APIs, especially
+	  HW-offload related.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called netdevsim.
+
 endif # NETDEVICES