Oracle datasource: secondary VNICs should use DHCP + routing-policy like EC2

On OCI, secondary VNICs currently get static-only config. This means: - Only `ipv6Addresses[0]` is configured, additional IPv6 addresses are dropped - No routing-policy rules, so outbound traffic from secondary VNIC IPs exits the primary interface and gets dropped by OCI's anti-spoofing - Users must hand-write a second netplan file for routes, routing-policy, and additional IPs Tested on VM.Standard.A1.Flex (Ubuntu 24.04): - OCI does not serve DHCPv4 on secondary VNICs (tested on two instances, 15s timeout each, no response) - OCI serves DHCPv6 on all VNICs — secondary VNICs get all assigned IPv6 addresses automatically - OCI's IMDS reports all IPv4 and IPv6 addresses per VNIC, plus subnet CIDRs - Routing-policy (`from: <ip>, table: <N>`) is required for secondary VNICs or outbound traffic is dropped The EC2 datasource already handles all of this (`DataSourceEc2.py:1065-1186`): - `dhcp4: true` on every NIC, not just primary - `dhcp6: true` when IPv6 addresses exist - Per-IP routing-policy rules on non-primary NICs with `table: 100 + nic_idx` - Additional static addresses via `get_secondary_addresses()` - Single-NIC cleanup (strips unnecessary overrides) Oracle's datasource should follow the same pattern, adapted for OCI's DHCP behavior (no DHCPv4 on secondary, DHCPv6 on all). We have a working v2-based implementation locally. Happy to PR if there's interest.