CVE-2026-63918 l2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname

In the Linux kernel, the following vulnerability has been resolved: l2tp: use refcountincnotzero in l2tpsessiongetbyifname A reader in l2tpsessiongetbyifname can return a pointer to a session whose refcount has reached zero. The getter takes its reference with plain refcountinc, but every other...