jwhited
Add large communities decoder and fix local pref attribute flag validation
I'm evaluating corebgp for use in a small project. When I last looked at this package maybe a year ago I noticed that it had no native ability to decode update messages so i resolved this by pulling in some functions/types from gobgp. Thank you for adding native decoding! For my use case I need to be able to decode large communities so this change adds that since it appears it was missing. Additionally I observed that the local preference decoder was not correctly validating attribute flags. Local pref is a well-known attribute which means the transitive flag must be set to 1 and all other flags are 0:
It looks like this was incorrectly set to expecting the optional flag as 1 (true) and transitive as 0 (false) so I fixed this and added some test cases.
Lastly, I added some simple changes to the example decoder to show how to decode/display MED, Local Pref and Large Communities.
