Deflake IptablesRestoreControllerTest.TestMemoryLeak.

* Increase the acceptable number of pages. With the current setting, the
  test fails in ~1% runs.
* Perform calculations in a signed type to handle the (rare) case when
  RSS goes down for whatever reason.

Bug: 162925719
Test: IptablesRestoreControllerTest.TestMemoryLeak
Change-Id: I2d3f3333feabb49d9ed19651d7339a1f275010ea
1 file changed