bpf: Support bpf_setsockopt() for BPF_CGROUP_INET_SOCK_CREATE.

bpf: Support bpf_setsockopt() for BPF_CGROUP_INET_SOCK_CREATE.

We will support flagging sk->sk_bypass_prot_mem via bpf_setsockopt()
at the BPF_CGROUP_INET_SOCK_CREATE hook.

BPF_CGROUP_INET_SOCK_CREATE is invoked by __cgroup_bpf_run_filter_sk()
that passes a pointer to struct sock to the bpf prog as void *ctx.

But there are no bpf_func_proto for bpf_setsockopt() that receives
the ctx as a pointer to struct sock.

Also, bpf_getsockopt() will be necessary for a cgroup with multiple
bpf progs running.

Let's add new bpf_setsockopt() and bpf_getsockopt() variants for
BPF_CGROUP_INET_SOCK_CREATE.

Note that inet_create() is not under lock_sock() and has the same
semantics with bpf_lsm_unlocked_sockopt_hooks.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Link: https://patch.msgid.link/20251014235604.3057003-5-kuniyu@google.com