Merge "fastboot: Use asynchronous operations to send data" into main am: 277533b7a3

Original change: https://android-review.googlesource.com/c/platform/system/core/+/2953831

Change-Id: Ic9a6d6dbd92ba9ff827cdf63283c7d6ef25f8d56
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>