Growable NetworkStats object instead of builder.

NetworkStats now grows in place with arraycopy() instead of callers
needing to know record count a priori.  Better growth calculation for
both NetworkStats and NetworkStatsHistory; 50% each time.  Better
estimates of buckets needed in calling services.

Change-Id: I3adbffa0b7407612cc6349d9135a8b4eb63cd440