batman-adv: avoid OGM aggregation when skb tailroom is insufficient

In the Linux kernel, the following vulnerability has been resolved:

batman-adv: avoid OGM aggregation when skb tailroom is insufficient

When OGM aggregation state is toggled at runtime, an existing forwarded

packet may have been allocated with only packet_len bytes, while a later

packet can still be selected for aggregation. Appending in this case can

hit skb_put overflow conditions.

Reject aggregation when the target skb tailroom cannot accommodate the new

packet. The caller then falls back to creating a new forward packet

instead of appending.