Update DscpPolicyTest to use random IPv6 prefixes.

Test: test-only change
Bug: 235559605
Change-Id: I47666abf51cd9939e1e16d056fdf8f2d468e5024
Merged-In: I47666abf51cd9939e1e16d056fdf8f2d468e5024
(cherry picked from commit 9f94e79c89db15016a1644ebfff7cea23fca1f1a)
1 file changed