[vendor-info] add vendor OUI support (#12991)

This commit introduces support for configuring and retrieving a vendor
OUI-24 (Organizationally Unique Identifier). It defines the new
`OPENTHREAD_CONFIG_NET_DIAG_VENDOR_OUI` configuration option and adds
the `otThreadGetVendorOui()` and `otThreadSetVendorOui()` APIs.

When specified, the vendor OUI is included in the `BorderAgent`
mDNS/DNS-SD TXT data under the `vo` key.

The `VendorInfo` class is updated to manage the OUI value. This
commit also adds the `vendor oui` CLI command to get or set this
property. Finally, it updates the tests to validate the presence and
correctness of the new `vo` key in the TXT data.

tests/nexus/openthread-core-nexus-config.h

@@ -125,6 +125,7 @@
 #define OPENTHREAD_CONFIG_NET_DIAG_VENDOR_MODEL "Nexus Simulation"
 #define OPENTHREAD_CONFIG_NET_DIAG_VENDOR_NAME "RD:OpenThread by Google Nest"
 #define OPENTHREAD_CONFIG_NET_DIAG_VENDOR_SW_VERSION "OT-simul-nexus"
+#define OPENTHREAD_CONFIG_NET_DIAG_VENDOR_OUI 0x020100
 #define OPENTHREAD_CONFIG_NETDATA_PUBLISHER_ENABLE 1
 #define OPENTHREAD_CONFIG_NUM_MESSAGE_BUFFERS 256
 #define OPENTHREAD_CONFIG_PARENT_SEARCH_BACKOFF_INTERVAL (10 * 60)

tests/nexus/test_border_agent.cpp

@@ -1461,6 +1461,14 @@ void ValidateMeshCoPTxtData(TxtData &aTxtData, Node &aNode, bool aExpectVendorIn
         aTxtData.ValidateKey("mn", expectedModelName);
         VerifyOrQuit(info.mHasModelName);
         VerifyOrQuit(StringMatch(info.mModelName, expectedModelName));
+
+        if (aNode.Get<VendorInfo>().IsOuiSpecified())
+        {
+            uint8_t ouiData[3];
+
+            BigEndian::WriteUint24(aNode.Get<VendorInfo>().GetOui(), ouiData);
+            aTxtData.ValidateKey("vo", ouiData);
+        }
     }
     else
     {