CVE-2026-72230: batman-adv: frag: free unfragmentable packet

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

batman-adv: frag: free unfragmentable packet

The caller of batadvfragsendpacket() assume that the skb provided to the function are always consumed. But the pre-check for an empty payload or the zero fragment size returned an error without any further actions.

A failed pre-check must use the same error handling code as the rest of the function.