=act #3680 fix SuspendReading being overruled by racy ChannelReadable
(cherry picked from commit 3da7f4ee074d2da8ffccb55f4ba6b3625b28e495)
Merge pull request #1796 from jrudolph/i/3680/fix-SuspendReading-race-backport

(backport) =act #3680 fix SuspendReading being overruled by racy ChannelReadable