Add TapPacketReader#startAsyncForTest, poll am: 046d253d63 am: 97825354b8

Original change: https://android-review.googlesource.com/c/platform/frameworks/libs/net/+/1435132

Change-Id: I437dac2c393e77d17ffbe81e3ace1697031fd8da
tree: 225cba0c582e4edeac687c2cfe3bc8d9d44bdda4
  1. staticlibs/