Increase ClusterPartition buffers to support farming of large files

The receive buffers in the cluster-service.xml UDP protocol are only 150K. Farming sends files around the cluster in 512K chunks. With the default config, the receive buffer sizes are not even large enough to hold one chunk. This can lead to problems where the packets that make up part of a chunk get dropped and have to be retransmitted. With very large files, this can slow things down to the point that timeouts start getting tripped and the transfer fails.

We had a support case where increasing the buffers to the sizes used by the fc-fast-minimalthreads config took care of the problem. That config uses 25MB receive buffers and 640K send buffers for both mcast and unicast; don't think we need to increase to such a high number for this. But, I will bump the send buffers to 640K and the receives to 2MB.