Increate netpolicy history size.

This is going to increase system_server's memory
footprint by ~40KB but without increasing this size,
we're not able to capture more than a couple of seconds
of events which makes it difficult to understand what's
going on in the bugs like b/114466242, b/112485285.

Bug: 111890351
Test: manual
Change-Id: I4484d6535adf869921e6cba32d0564934448c3b1