Fix flaky IpPrefixTest.

Test: IpPrefixTest passes
Bug: 32561414
Merged-In: Ib4bffe9d33a6d4f5c2bd97798073de0f66d77645

(cherry pick from commit 32c687040301cb3601fd110281a742159a963aa9)

Change-Id: Ibaf11aae9b13af868bebff820c9e7615b63c8eb2
1 file changed