Revert "Skip functional l3 agent test"

This reverts commit 0918ce91e5af5100ee3a4fcd6861741c4f00ac41. The
specified commit skipped a test which caused non-deterministic gate
failures, but the actual reason for the failures was found and fixed
so the skip is no longer needed.

Related-bug: #1358206
Related-bug: #1364171
Change-Id: I9b0d9ad9ad8b62ee92877fc0a6db0323604433ac
Merge "Revert "Skip functional l3 agent test""