In some deployments, the "neutron" user does not have the permissions
to modify the kernel interfaces. In those cases the radvd user should
be defined. This patch introduces a new config option: "radvd_user".
This config option is the username passed to radvd, used to drop root
privileges and change user ID to username and group ID to the primary
group of username. If no user specified (by default is an empty string),
the user executing the L3 agent will be passed. If "root" specified,
because radvd is spawned as root, no "username" parameter will be
passed.
Change-Id: Ie9a6fbf04d453a3c1c0bddf9ecaa3d4d6467e8ff
Closes-Bug: #1844688
(cherry picked from commit 6a5a75d5a6)
6ec7ba8695