macs: ignore duplicate MAC for devs with driver igc

[xanthein]

Add igc to duplicate MAC ignore list, fix #6782

Proposed Commit Message

In factory production, customer needs to login to the Ubuntu desktop
 or console before using the tool to flash the MAC address. we should 
ignore the duplicate mac exception in this case.

Fixes #6782 
LP: #2142651

Additional Context

Test Steps

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[blackboxsw]

Thank you @xanthein for the submission to cloud-init.
I think we will need a bit of unit test coverage before we can land this

diff --git a/tests/unittests/test_net.py b/tests/unittests/test_net.py
index 5b92ba280..338fc36dc 100644
--- a/tests/unittests/test_net.py
+++ b/tests/unittests/test_net.py
@@ -5658,7 +5658,9 @@ class TestGetInterfacesByMac:
         assert expected == result
 
 
-@pytest.mark.parametrize("driver", ("mscc_felix", "fsl_enetc", "qmi_wwan"))
+@pytest.mark.parametrize(
+    "driver", ("igc", "mscc_felix", "fsl_enetc", "qmi_wwan")
+)
 @mock.patch("cloudinit.net.get_sys_class_path")
 @mock.patch("cloudinit.util.system_info", return_value={"variant": "ubuntu"})
 class TestDuplicateMac:

[holmanb]

I don't think that we can accept this proposal. Any system that has a single interface that uses this driver would be unable to boot with cloud-init. Searching online, I found at least one motherboard like this.