fix: query both the vendor and OEM fields at the redfish base root to determine a BMC's vendor (#2761)

<!-- Describe what this PR does -->
fix: some supermicros do not report the vendor at the raw vendor field
at the base redfish root. instead, they report the vendor as SMC at the
OEM field. use the vendor() func to determine the vendor from the BMC as
it checks both the raw vendor and oem fields as a fallback. fixes:
6338388

## Related issues
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## Type of Change
<!-- Check one that best describes this PR -->
- [ ] **Add** - New feature or capability
- [ ] **Change** - Changes in existing functionality
- [ ] **Fix** - Bug fixes
- [ ] **Remove** - Removed features or deprecated functionality
- [ ] **Internal** - Internal changes (refactoring, tests, docs, etc.)

## Breaking Changes
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<!-- Breaking changes are not generally permitted, please discuss on a
GitHub discussion or with the development team if you believe you need
to break a backward compatibility guarantee -->
- [ ] **This PR contains breaking changes**

## Testing
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- [ ] Unit tests added/updated
- [ ] Integration tests added/updated
- [ ] Manual testing performed
- [ ] No testing required (docs, internal refactor, etc.)

## Additional Notes
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Author: spydaNVIDIA

crates/site-explorer/src/redfish.rs

@@ -130,16 +130,18 @@ impl RedfishClient {
 
         let service_root = client.get_service_root().await.map_err(map_redfish_error)?;
 
-        if service_root.vendor.is_none() {
-            return Err(EndpointExplorationError::MissingVendor);
+        // Do not gate on the raw `Vendor` field: some BMCs (e.g. Supermicro
+        // SYS-121H-TNR) leave ServiceRoot.Vendor null but still identify
+        // themselves via the `Oem` key. libredfish's `vendor()` already
+        // consults Oem as a fallback, so resolve through it and only reject
+        // when the result is genuinely unrecognized. See NVBug 6338388.
+        match service_root.vendor() {
+            Some(vendor) if vendor != RedfishVendor::Unknown => Ok(vendor),
+            _ => {
+                tracing::info!("No recognized vendor for BMC at {bmc_ip_address}");
+                Err(EndpointExplorationError::MissingVendor)
+            }
         }
-
-        let Some(vendor) = service_root.vendor() else {
-            tracing::info!("No vendor found for BMC at {bmc_ip_address}");
-            return Err(EndpointExplorationError::MissingVendor);
-        };
-
-        Ok(vendor)
     }
 
     pub async fn validate_bmc_credentials(