nf_getsockopt
int nf_getsockopt(struct sock *sk, u_int8_t pf, int optval, char __user *opt,
err = nf_getsockopt(sk, PF_INET, optname, optval, &len);
err = nf_getsockopt(sk, PF_INET6, optname, optval, &len);
EXPORT_SYMBOL(nf_getsockopt);