fix(network-legacy): always include af_packet

fix(network-legacy): always include af_packet

For static IPv4 configurations, we use arping to check for duplicate
IP addresses. arping requires the af_packet module to work, and if arping
fails, the IP address will not be set and booting will fail.
af_packet may not be loaded / required in the running system, for example if
the system had been booted in an IPv6 configuration, or if it had been
manually unloaded. Make sure it's included in initramfs in hostonly mode, too.