USBForward: asynchronous operations, stage 2

- provide a thread for libusb to execute asynchronous operations,
- allow libusb to allocate transfer (otherwise it will just discard
  request),
- move LOG_TAG to makefile

BUG=64121751
Change-Id: I57031f2554f79b77dcc28c28e065942b0966177f
6 files changed
tree: 9a555429367638d1b7b830a862142344d9581d8a
  1. common/
  2. external/
  3. guest/
  4. host/
  5. tools/
  6. WORKSPACE