Make ssync_receiver drop conn on exc

Before, the ssync receiver wouldn't hang up the connection with all
errors. Now it will. Hanging up early will ensure the remote end gets
a "broken pipe" type error right away instead of it possible sending
more data for quite some time before finally reading the error.

Change-Id: I2d3d55baaf10f99e7edce7843a7106875752020a
Merge "Make ssync_receiver drop conn on exc"