adb: properly calculate packet size on Mac.

OS X reports maxPacketSize as wMaxPacketSize * (bMaxBurst + 1) in the
deprecated GetPipeProperties function. Use the also-deprecated
GetPipePropetiesV2 API to get bMaxBurst and figure out what
wMaxPacketSize is. (This file is going to go away eventually, so don't
bother with switching to the recommended GetPipePropertiesV3, since
it would be a substantially larger charge.)

libusb is unaffected.

Bug: http://b/77733422
Test: python test_device.py
Change-Id: I66517d699a4f39b93ba5eb7882bd8ee6c70f3672