bpf, vsock: Fix poll() missing a queue

When a verdict program simply passes a packet without redirection, sk_msg
is enqueued on sk_psock::ingress_msg. Add a missing check to poll().

Fixes: 634f1a71 ("vsock: support sockmap")
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
Link: https://lore.kernel.org/r/20241118-vsock-bpf-poll-close-v1-1-f1b9669cacdc@rbox.co


Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>