usb: misc: usbtest: format max packet size for iso transfer

The current code prints all wMaxPacketSize content at endpoint
descriptor, if there is a high speed, high bandwidth endpoint,
it may confuse the users, eg, if there are 3 transactions during
microframe, it will print "wMaxPacket 1400" for packet content.
This commit splits wMaxpacketSize and transaction numbers for
output messages.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>