message: Let AsyncUDPSocket send to multiple addresses
  Summary:
  Add support for variable number of addrs so we can send data to multiple destinations.
  (Note: this ignores all push blocking failures!)
diff: @@ -134,7 +134,8 @@ ssize_t SendmmsgPacketBatchWriter::write(
  return sock.write(address, bufs_[0]);
  }
  - int ret = sock.writem(address, bufs_.data(), bufs_.size());
  + int ret = sock.writem(
  + folly::range(&address, &address + 1), bufs_.data(), bufs_.size());
  if (ret <= 0) {
  return ret;
  @@ -219,7 +220,11 @@ ssize_t SendmmsgGSOPacketBatchWriter::write(
  : sock.write(address, bufs_[0]);
  }
  - int ret = sock.writemGSO(address, bufs_.data(), bufs_.size(), gso_.data());
  + int ret = sock.writemGSO(
  + folly::range(&address, &address + 1),
  + bufs_.data(),
  + bufs_.size(),
  + gso_.data());
  if (ret <= 0) {
  return ret;
  