vsock/vmci: log once the failed queue pair allocation

VMCI feature is not supported in conjunction with the vSphere Fault
Tolerance (FT) feature.

VMware Tools can repeatedly try to create a vsock connection. If FT is
enabled the kernel logs is flooded with the following messages:

    qp_alloc_hypercall result = -20
    Could not attach to queue pair with -20

"qp_alloc_hypercall result = -20" was hidden by commit e8266c4c
("VMCI: Stop log spew when qp allocation isn't possible"), but "Could
not attach to queue pair with -20" is still there flooding the log.

Since the error message can be useful in some cases, print it only once.

Fixes: d021c344 ("VSOCK: Introduce VM Sockets")
Signed-off-by: NStefano Garzarella <sgarzare@redhat.com>
Reviewed-by: NJorgen Hansen <jhansen@vmware.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/vmw_vsock/vmci_transport.c

@@ -568,8 +568,7 @@ vmci_transport_queue_pair_alloc(struct vmci_qp **qpair,
 			       peer, flags, VMCI_NO_PRIVILEGE_FLAGS);
 out:
 	if (err < 0) {
-		pr_err("Could not attach to queue pair with %d\n",
-		       err);
+		pr_err_once("Could not attach to queue pair with %d\n", err);
 		err = vmci_transport_error_to_vsock_error(err);
 	}