Reapply "Test Updating OUTPUT_MARK on Active SAs"

This reverts commit dd2d3198.
Thus reapplying commit 4406bae0.

Original commit log:

Test Updating OUTPUT_MARK on Active SAs

Test that the xfrm output mark is update-able
on an Active SA, which means that we can dynamically
reroute traffic to new underlying networks after an
SA has been created.

Bug: 71645364
Change-Id: I78c67001c63e2c82bf1f6e87af4efce855d34269
Test: run_net_test.sh xfrm_test.py