net: lapb: increase LAPB_HEADER_LEN

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DEBIAN-CVE-2024-56659

In the Linux kernel, the following vulnerability has been resolved: net: lapb: increase LAPBHEADERLEN It is unclear if net/lapb code is supposed to be ready for 8021q. We can at least avoid crashes like the following : skbuff: skbunderpanic: text:ffffffff8aabe1f6 len:24 put:20 head:ffff88802824a4...