CASSANDRA-18400: Nodetool info should report on the new networking cache

[qannap]

CASSANDRA-18400: Nodetool info should report on the new networking cache

1. The Network Cache info looks like this:

Network Cache : size ? MiB, capacity ? MiB
The capacity is the network cache total threshold, which corresponds to NETWORKING_MEMORY_USAGE_THRESHOLD, and the size is the size of allocated pooled buffers.

2. The NaN hit rate in the row, and the counter cache is caused by dividing by zero, but the zero comes from zero requests. In this case, I changed the hit rate to 0 when the hit rate was NaN. I am not sure if it is valid to do that.

patch by Ningzi Zhan

The Cassandra Jira