CVE-2024-38566 bpf: Fix verifier assumptions about socket->sk

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

bpf: Fix verifier assumptions about socket->sk

The verifier assumes that ‘sk’ field in ‘struct socket’ is valid
and non-NULL when ‘socket’ pointer itself is trusted and non-NULL.
That may not be the case when socket was just created and
passed to LSM socket_accept hook.
Fix this verifier assumption and adjust tests.