batman-adv: reduce local TT entry timeout to 10 minutes

The current timeout is set to one hour. However a client connected to the mesh
network will always generate traffic. In the worst case it will send ARP
requests every 4 or 5 minutes. On the other hand having a long timeout means
storing dead entries for one hour and it leads to very big trans-tables
containing useless clients.

This patch reduces the timeout to 10 minutes

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>