A minor followup change for BPF offload device option stuff

- Correct description and spelling in the code and xml files.
- Add a TODO for refactoring the IpServer constructor.
- Refine the if-statement for starting IP neighbor monitor.

Bug: 149997301
Test: atest IpServerTest
Original-Change: https://android-review.googlesource.com/1309273
Merged-In: If9c8bc6f785fa80575db56de4e223292e9807ace
Change-Id: If9c8bc6f785fa80575db56de4e223292e9807ace