batman-adv: throughput meter implementation

The throughput meter module is a simple, kernel-space replacement for
throughtput measurements tool like iperf and netperf. It is intended to
approximate TCP behaviour.

It is invoked through batctl: the protocol is connection oriented, with
cumulative acknowledgment and a dynamic-size sliding window.

The test *can* be interrupted by batctl. A receiver side timeout avoids
unlimited waitings for sender packets: after one second of inactivity, the
receiver abort the ongoing test.

Based on a prototype from Edo Monticelli <montik@autistici.org>

Signed-off-by: Antonio Quartulli <antonio.quartulli@open-mesh.com>
Signed-off-by: Sven Eckelmann <sven.eckelmann@open-mesh.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>