CVE-2026-72226: batman-adv: tt: prevent TVLV OOB check overflow

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

batman-adv: tt: prevent TVLV OOB check overflow

A TT unicast TVLV contains the number of VLANs stored in it. This number is an u16 and gets multiplied by the size of the struct batadvtvlvttvlandata (8 bytes). The size can therefore overflow the u16 used to store the ttvlanlen. All additional safety checks to prevent out-of-bounds access of the TVLV buffer are invalid due to this overflow.

Using sizet prevents this overflow and ensures that the safety checks compare against the actual buffer requirements.