Consistency: make default max_hint_window_in_ms actually 3 hours

From IRC/#cassandra:

CASSANDRA-4632 changed max_hint_window_in_ms from 1 hour to 3 hours, however, it only changed the default in cassandra.yaml - it left the actual default in Config.java at 1 hour.

This issue is to update Config.java for consistency, in case users comment out the actual entry in cassandra.yaml and revert to the "real" default of 1 hour.