adb: disable USB packet overflow checking on OS X.

OS X appears to be misreporting the maximum packet size on some
hardware. Disable this on OS X until we figure out what's going on.

Bug: http://b/65063965
Bug: https://issuetracker.google.com/70244520
Test: python test_device.py on linux with CHECK_PACKET_OVERFLOW disabled
Test: python test_device.py on darwin (but on hardware that wasn't reproducing this)
Change-Id: I57e1adfa162e40ed79f71f97af552b3f0519324e