staging: usbip: userspace: usbip list: move output header

Delay the printing of the output header until the list is received
from the remote host. This allows notification that the host does not
have any exportable devices.

Signed-off-by: matt mooney <mfm@muteddisk.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>