[CommCoreModule] Simplify matchesInboundSession return logic

Summary: Minor thing I noticed when working in CryptoModule.cpp

Test Plan: Close reading.. logic should be identical

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

Reviewed By: palys-swm, ashoat

Subscribers: benschac, ashoat, Adrian

Differential Revision: https://phabricator.ashoat.com/D3269