[net_server] disabling IPv6 also disables IPv4 after reboot

[diver]

This is hrev56385 x86_64 in vmware.

Network preflet default state:
IPv4 mode is set to DHCP, IPv6 is set to Automatic.

/system/settings/network/interfaces

interface	/dev/net/pcnet/0 {
	address	inet6
	address	inet {
		auto_config	true
	}
}

Disabling IPv6 triggers IPv4 reconfiguration, also IPv6 mode changes back to Automatic.
However, after a reboot both interfaces are disabled:

interface	/dev/net/pcnet/0 {
	address	inet6
	address	inet
}