batman-adv: fix tt_local_reset_flags() function

    tt_local_num has to be increased only the when flag passed as argument is reset.
    Currently the couter 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 containing a copy of non-initialised memory thus corrupting other
    nodes global translation table and making higher level communication impossible.
    This is an important fix and need to be committed as soon as possible.

    Reported-by: Junkeun Song <jun361@gmail.com>
    Signed-off-by: Antonio Quartulli <ordex@autistici.org>