[make] Add qemu-e1000 target

- qemu target will have no default network interface besides any ax8872b
  it can disconnect from the host.
- qemu-e1000 target will use tap to connect an e1000 interface to
  an existing tun interface named qemu. NOTES.txt explains this more.

Change-Id: I45709dac964ef0ffaa1f849cf9adb2ca8ac3a5c1
1 file changed