[CommCoreModule] Set readyState to SocketStatus::CLOSING on call to ClientGetReadReactor::close()

Summary: We don't really distinguish between 2: CLOSING and 3: CLOSED in lib/socket.react.js, but don't think it hurts to add this here.

Test Plan: Logged readyState

Reviewers: ashoat, palys-swm, def-au1t, varun, karol-bisztyga, jimpo

Reviewed By: ashoat, karol-bisztyga

Subscribers: Adrian, benschac

Differential Revision: https://phabricator.ashoat.com/D3120