rtnl: support adding VETH_INFO_PEER containers into rtnl messages
nspawn: add new --network-veth switch to add a virtual ethernet link to the host
nspawn: make socket(AF_NETLINK, *, NETLINK_AUDIT) fail with EAFNOTSUPPORT in containers

The kernel still doesn't support audit in containers, so let's make use
of seccomp and simply turn it off entirely. We can get rid of this big
as soon as the kernel is fixed again.
logind: make sure to terminate systemd user on logouts

Currently if the user logs out, the GC may never call user_stop(),
this will not terminate the systemd user and (sd-pam) of that user.

To fix this, remove the USER_CLOSING state check that is blocking the
GC from calling user_stop(). Since if user_check_gc() returns false
this means that all the sessions of the user were removed which will
make user_get_state() return USER_CLOSING.

Conclusion: that test will never be statisfied.

So we remove the USER_CLOSING check and replace it with a check inside
user_stop() this way we know that user_stop() has already queued stop
jobs, no need to redo.

This ensures that the GC will get its two steps correctly as pointed out
by Lennart:
http://lists.freedesktop.org/archives/systemd-devel/2014-February/016825.html

Note: this also fixes another bug that prevents creating the user
private dbus socket which will break communications with the user
manager.