Clarify UsbConnection#bulkTransfer api behavior

- Do not allow negative length as inside of JNI this is interpreted as
  unsigned value which lead to memory corruptions.
- Document behavior for uncommon but usable values of parameters

Test: Ran CTS verifier UBS device test
Change-Id: I0899a2831c6dd2617528a5e79ea21932f6a66c13
1 file changed