Resolve "Some paths of a device cant be requested more than once"

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Closes #147 (closed)

nucleus/southbound.go

@@ -114,7 +114,10 @@ func unmarshal(schema *ytypes.Schema, bytes []byte, fields []string, goStruct yg
 		return err
 	}
 	ygot.PruneEmptyBranches(validatedDeepCopy)
-	return ygot.MergeStructInto(goStruct, validatedDeepCopy)
+
+	opts := []ygot.MergeOpt{&ygot.MergeOverwriteExistingFields{}}
+
+	return ygot.MergeStructInto(goStruct, validatedDeepCopy, opts...)
 }
 
 // getField traverses the GoStruct and returns the field that represents the