DataSourceOracle: prefer DS network config over initramfs

The Oracle platform provides networking configuration from two sources:

* the primary interface configuration comes from the initramfs, because
  Oracle instance all iSCSI boot
* secondary interface configuration comes from an IMDS accessed over
  HTTP

As we need to combine these two sources of network configuration, the
default "prefer initramfs config over data source config" behaviour
isn't appropriate; we would never get the IMDS interfaces via that
route.  Instead, the Oracle data source has code to combine these two
sources, so we prefer its network configuration over the initramfs
configuration.

(This is not appropriate default behaviour, because _in general_ data
sources won't know how to merge initramfs-provided configuration into
their provided configuration, so switching this order for all data
sources would result in initramfs configuration being discarded on any
data source that implements network_config.)

cloudinit/sources/DataSourceOracle.py

@@ -109,6 +109,13 @@ class DataSourceOracle(sources.DataSource):
     dsname = 'Oracle'
     system_uuid = None
     vendordata_pure = None
+    network_config_sources = (
+        sources.NetworkConfigSource.cmdline,
+        sources.NetworkConfigSource.ds,
+        sources.NetworkConfigSource.initramfs,
+        sources.NetworkConfigSource.system_cfg,
+    )
+
     _network_config = sources.UNSET
 
     def __init__(self, sys_cfg, *args, **kwargs):

cloudinit/sources/tests/test_oracle.py

@@ -1,7 +1,7 @@
 # This file is part of cloud-init. See LICENSE file for license information.
 
 from cloudinit.sources import DataSourceOracle as oracle
-from cloudinit.sources import BrokenMetadata
+from cloudinit.sources import BrokenMetadata, NetworkConfigSource
 from cloudinit import helpers
 
 from cloudinit.tests import helpers as test_helpers
@@ -303,6 +303,14 @@ def test_secondary_nic_failure_isnt_blocking(
         self.assertIn('Failed to fetch secondary network configuration',
                       self.logs.getvalue())
 
+    def test_ds_network_cfg_preferred_over_initramfs(self):
+        """Ensure that DS net config is preferred over initramfs config"""
+        network_config_sources = oracle.DataSourceOracle.network_config_sources
+        self.assertLess(
+            network_config_sources.index(NetworkConfigSource.ds),
+            network_config_sources.index(NetworkConfigSource.initramfs)
+        )
+
 
 @mock.patch(DS_PATH + "._read_system_uuid", return_value=str(uuid.uuid4()))
 class TestReadMetaData(test_helpers.HttprettyTestCase):