firewalld: Add routines to firewalld to mark traffic and masquerade

This CL adds routines to firewalld that enable network traffic to
be marked based on user id and masquerading rules for network
interfaces.

BUG=chromium:458075
TEST=Manual testing

Change-Id: I81e08f1c20bf99887ac87c9970fcc2a58dcd2355
Reviewed-on: https://chromium-review.googlesource.com/249111
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Tested-by: Prabhu Kaliamoorthi <kaliamoorthi@chromium.org>
Commit-Queue: Prabhu Kaliamoorthi <kaliamoorthi@chromium.org>
3 files changed