batman-adv: fix skb->data assignment

commit 2c995ff892313009e336ecc8ec3411022f5b1c39 upstream.

skb_linearize(skb) possibly rearranges the skb internal data and then changes
the skb->data pointer value. For this reason any other pointer in the code that
was assigned skb->data before invoking skb_linearise(skb) must be re-assigned.

In the current tt_query message handling code this is not done and therefore, in
case of skb linearization, the pointer used to handle the packet header ends up
in pointing to free'd memory.

This bug was introduced by a73105b8d4c765d9ebfb664d0a66802127d8e4c7
(batman-adv: improved client announcement mechanism)

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>