When an ack with a sequence number equal to the last_acked is received, the
dup_acks counter is increased to decide whether fast retransmit should be
performed. Only when the sequence numbers are not equal, the dup_acks is
set to the initial value (0).
But if the initial packet would have the sequence number
BATADV_TP_FIRST_SEQ, dup_acks would not be initialized and atomic_inc would
operate on an undefined starting value. It is therefore required to have it
explicitly initialized during the start of the sender session.
Cc: stable@kernel.org
Fixes: 33a3bb4a33 ("batman-adv: throughput meter implementation")
Signed-off-by: Sven Eckelmann <sven@narfation.org>