[MINOR] read optimizations based on the MSS

[MINOR] read optimizations based on the MSS

Generally, if a recv() returns less bytes than the MSS, it means that
there is nothing left in the system's buffers, and that it's not worth
trying to read again because we are very likely to get nothing. A
default read low limit has been set to 1460 bytes below which we stop
reading.

This has brought a little speed boost on small objects while maintaining
the same speed on large objects.