Document IPAddressV6 Class
Document IPAddressV6 Class

Summary:
Add doxygen comments to `IPAddressv6.h`

(Note: this ignores all push blocking failures!)

Reviewed By: Gownta

Differential Revision: D39058429

fbshipit-source-id: f6e38f8efec55de9d4b37f2c4adf9644aa080bda

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly