vyos-hostsd: T2583: update systemd service
vyos-hostsd: T2583: update systemd service

- set RuntimeDirectory to vyos-hostsd
- set RuntimeDirectoryPreserve in order to not delete the state file between
  service restarts (/run will be deleted across reboots as it's on a tmpfs but
  the state doesn't need to be saved across reboots anyway)
- set WorkingDirectory to /run/vyos-hostsd

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x