batman-adv: fix tt_local_reset_flags() function

Currently the counter of tt_local_entry structures (tt_local_num) is incremented
each time the tt_local_reset_flags() is invoked causing the node to send wrong
TT_REPONSE packets containing a copy of non-initialised memory thus corrupting
other nodes global translation table and making higher level communication
impossible.

Reported-by: Junkeun Song <jun361@gmail.com>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Acked-by: Junkeun Song <jun361@gmail.com>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>