usb-redir: allocate buffers before waking up the host adapter

Needed to make sure usb redirection is prepared to actually handle the
callback from the usb host adapter.  Without this interrupt endpoints
don't work on xhci.

Note: On ehci the usb_wakeup() call only schedules a BH for the actual
work, which hides this bug because the allocation happens before ehci
calls back even without this patch.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Message-id: 1476096313-7730-1-git-send-email-kraxel@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>