setOnRecv must lock socketsMutex. Generally it,s the case because onAccept
will be ready right away and still locked, however if onChannelReady_ retrigger
the callback, setOnRecv will be used without socketsMutex locked.

Retrigger in a thread and always lock socketsMutex to be sure.

Change-Id: If44d240e113585a5ce3320b8f17feaaaa8be8515