Refactor linkstate serializeNlri methods

Currently there are 3 methods in LinkstateNlriParser that somehow serialize Linkstate destination object"

1. public static void serializeNlri(final CLinkstateDestination destination, final ByteBuf buffer)

2. public static void serializeNlri(final UnkeyedListEntryNode linkstate, final ByteBuf buffer)

3. public static CLinkstateDestination setLinkstateDestination(final MapEntryNode route)

We need one method that will arse CLinkstateDestination from DOM representation and if necessary it will call the first method to serialize the result to bytes.