Provide stronger memory safety guarantee around NDP options

[drunkirishcoder]

Describe the bug?

When working with NDP options, either by pushing a new one or parsing through the existing ones, the option structs returned can be independently owned. That, of course, breaks the memory safety guarantee that you can't have multiple mutable references to the same object.

Expected behavior?

The options returned should behave as if they are mutable borrows on the packet.