Fix flaky IpMemoryStoreServiceTest.testFullMaintenance/testInterruptMaintenance

These two tests failed due to running over than 60s. The reason
is too many fake data that need to insert into database. It will
take long time and cause test time out. So preload the data base
with fake data to save the I/O operation time which can reduce
testing time for these tests.

Fix: 140538459
Test: atest NetworkStackTests on both CF and P3
Change-Id: Iac30a2be933ed10450f0704075f08d10c1886986