Refactor RA parsing code for simplicity.

Currently, the RA parsing code keeps track of byte ranges in the
packet using pairs of integers called "non-lifetimes". Replace
this with a PacketSection class that also stores some information
about the range including whether the range should be matched or
not, what ICMP option the section was a part of, and so on.

This makes the code easier to read and will make it easier to
change the behaviour based on the information contained in the
sections.

Bug: 66928272
Test: refactoring covered by existing unit tests
Change-Id: Iab8b04aafce8d8992e835a6448a75b950296bec5