Make the buffer size in AvailableReader depend on packet sizes the client is using + introduce read timeouts

[jstuczyn]

When the client transmission rate is small, measured at the Poisson process, then a large buffer size causes large latencies for the connected application when sending large chunks of data, make the connection unreliable.

Reducing the buffer size, ideally while making it a multiple of the capacity of the select sphinx packet size, should solve this