Staging: batman-adv: Limit queue lengths for batman and broadcast packets

Staging: batman-adv: Limit queue lengths for batman and broadcast packets

This patch limits the queue lengths of batman and broadcast packets. BATMAN
packets are held back for aggregation and jittered to avoid interferences.
Broadcast packets are stored to be sent out multiple times to increase
the probability to be received by other nodes in lossy environments.

Especially in extreme cases like broadcast storms, the queues have been seen
to run full, eating up all the memory and triggering the infamous OOM killer.
With the queue length limits introduced in this patch, this problem is
avoided.

Each queue is limited to 256 entries for now, resulting in 1 MB of maximum
space available in total for typical setups (assuming one packet including
overhead does not require more than 2000 byte). This should also be reasonable
for smaller routers, otherwise the defines can be tweaked later.

This third version of the patch does not increase the local broadcast
sequence number when the queue is already full.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>