usb: core: allow isoc URBs for wireless devices with an interval < 6

In usb_submit_urb, do not fail if an isoc URB for a wireless USB device
has an interval < 6.  Per WUSB spec, isoc endpoints can support values
from 1-16.  Valid values for interrupt URBs for wireless USB devices are
still 6-16.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>