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: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Jorgen Hansen <jhansen@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>