systemd: check both OEM IDs for flatcar and coreos

For backwards compatibilities, we need to check both OEM IDs in the
kernel command line, `flatcar.oem.id` and `coreos.oem.id`.

systemd/network/yy-azure-sriov-coreos.network

@@ -0,0 +1,15 @@
+# Ignore SR-IOV interface on Azure, since it'll be transparently bonded
+# to the synthetic interface
+
+[Match]
+KernelCommandLine=coreos.oem.id=azure
+# With NetworkManager, Azure uses a udev rule matching DRIVERS=="hv_pci".
+# This won't work with networkd because it only checks the driver of the
+# device itself, not its parents. All we can do instead is blacklist the
+# VF driver currently used in Azure. If other drivers come into use, the
+# symptom will be a VF interface in the output of "networkctl" which never
+# finishes configuring.
+Driver=mlx4_en
+
+[Link]
+Unmanaged=yes