CVE-2026-72461: apparmor: fix refcount leak when updating the sk_ctx

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

apparmor: fix refcount leak when updating the skctx

Currently updateskctx() transfers the plabel reference, unfortunately it is also unconditionally put in the caller. Ideally we would make the caller conditionally put the reference based on whether it was transferred but for now just fix the bug by getting a reference.