[#356] netmap: Check for attribute duplicates in NodeInfo.readFromV2()

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

netmap/node_info_test.go

@@ -271,7 +271,6 @@ func TestNodeInfo_Unmarshal(t *testing.T) {
 			fmt.Sprintf("invalid %s attribute", attrCapacity))
 	})
 	t.Run("duplicate attributes", func(t *testing.T) {
-		t.Skip("FIXME")
 		n := goodNodeInfo()
 
 		var a netmap.Attribute