batman-adv: fix counter for multicast supporting nodes

batman-adv: fix counter for multicast supporting nodes

A miscounting of nodes having multicast optimizations enabled can lead
to multicast packet loss in the following scenario:

If the first OGM a node receives from another one has no multicast
optimizations support (no multicast tvlv) then we are missing to
increase the counter. This potentially leads to the wrong assumption
that we could safely use multicast optimizations.

Fixings this by increasing the counter if the initial OGM has the
multicast TVLV unset, too.

Introduced by 15bc72bd1e4945d93cac43ae6a2a017cae849fd9
("batman-adv: Announce new capability via multicast TVLV")

Reported-by: Tobias Hachmer <tobias@hachmer.de>
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>