vsock: fix recursive ->recvmsg calls

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

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().