设置 Linux 防火墙规则，以允许 Fuchsia 设备和模拟器流量。
Setup Linux firewall via iptables to allow Fuchsia device and emulator traffic.
This command detects whether iptables is installed,
and if so, will add special rules to allow Fuchsia-specific traffic to
go through the link-local IPv6 network interfaces used by Fuchsia devices
and emulators. If `ufw` (Uncomplicated Firewall) is installed on the system,
we will abort, and recommend the script `fx setup-ufw`.
NOTE: This script uses sudo and will thus ask for your password!
-n|--dry-run Just print all steps, don't do any configuration
-u|--undo Remove all firewall rules installed by this script