Cleanup of afamily/pfamily specs for Addrinfo#initialize

[herwinw]

It looks like there was a lot of copy-paste in this one, often the description did not match the actual test. The descriptions have been updated to use the shortest human readable syntax, so no Socket:: namespace and no PF_ prefix to the name. This matches the afamily specs (or: most of them).

Additionally, a few additional spaces in the descriptions have been removed.