vsock: fix recursive ->recvmsg calls

After a vsock socket has been added to a BPF sockmap, its prot->recvmsg
has been replaced with vsock_bpf_recvmsg(). Thus the following
recursiion could happen:

vsock_bpf_recvmsg()
 -> __vsock_recvmsg()
  -> vsock_connectible_recvmsg()
   -> prot->recvmsg()
    -> vsock_bpf_recvmsg() again

We need to fix it by calling the original ->recvmsg() without any BPF
sockmap logic in __vsock_recvmsg().

Fixes: 634f1a71 ("vsock: support sockmap")
Reported-by:  <syzbot+bdb4bd87b5e22058e2a4@syzkaller.appspotmail.com>
Tested-by:  <syzbot+bdb4bd87b5e22058e2a4@syzkaller.appspotmail.com>
Cc: Bobby Eshleman <bobby.eshleman@bytedance.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://patch.msgid.link/20240812022153.86512-1-xiyou.wangcong@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>