ec2: disable LLMNR in systemd-resolved

We use systemd-resolved in bookworm and newer, which enabled LLMNR by default. As this is not supported in EC2, we should consider disabling it there.

admin@i-0eef209789ffe8b9f:~$ resolvectl llmnr
Global: yes
Link 2 (ens5): yes

Not sure if this applies to other cloud environments, but I imagine it does.