batman-adv: fix multicast counter when purging originators

batman-adv: fix multicast counter when purging originators

When purging an orig_node we should only decrease counter tracking the
number of nodes without multicast optimizations support if it was
increased through this orig_node before.

A not yet quite initialized orig_node (meaning it did not have its turn
in the mcast-tvlv handler so far) which gets purged would not adhere to
this and will lead to a counter imbalance.

Fixing this by adding a check whether the orig_node is mcast-initalized
before decreasing the counter in the mcast-orig_node-purging routine.

Introduced by 60432d756cf06e597ef9da511402dd059b112447
("batman-adv: Announce new capability via multicast TVLV")

Reported-by: Tobias Hachmer <[email protected]>
Signed-off-by: Linus Lüssing <[email protected]>
Signed-off-by: Marek Lindner <[email protected]>
Signed-off-by: Antonio Quartulli <[email protected]>