selftests/bpf: fix a test for snprintf() overflow
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.4.211 by commit ecbdb2985e086b59faef68329688bc41f89c3398, it was introduced in version v4.18 by commit c0fa1b6c3efc64b4ecfec658f95475fda650742e. For more details please see the references link.