networkd: add support for peer address

This patch adds peer address support for
networkd . In the  [Address]  a new configurable
param is Peer.

[Match]
Name=ipip-tun

[Address]
Address=10.0.0.1/32
Peer=10.0.0.2/32
networkd: netdev - add missing refs

Without this, the underlying device would get freed (and hence
fail).
man: network - document Peer key
vconsole-setup: fix inverted error messages

Introduced in abee28c56d.

Pointed-out-by: Werner Fink <werner@suse.de>
udev: link_config - ignore errors due to missing MAC address

Otherwis, we get misleading error messages on links with MACs.

Reported by Leonid Isaev.
util: consider 0x7F a control chracter (which it is: DEL)

Let's better be safe than sorry.
main: explain our /etc empty check a bit in a comment
update TODO
shared: make timezone and locale enumeration and validation generic

This way we can reuse it other code thatn just localectl/localed +
timedatectl/timedated.
util: don't consider tabs special in string_has_cc() anymore

Instead, take a list of exceptions to our usual CC check
fileio: simplify write_env_file()
man: add missing archs to ConditionArchitecture= description
man: chroot jails are no longer detected by ConditionVirtualization=
architecture: add string table entries for mips-le archs which were missing
firstboot: add new component to query basic system settings on first boot, or when creating OS images offline

A new tool "systemd-firstboot" can be used either interactively on boot,
where it will query basic locale, timezone, hostname, root password
information and set it. Or it can be used non-interactively from the
command line when prepareing disk images for booting. When used
non-inertactively the tool can either copy settings from the host, or
take settings on the command line.

$ systemd-firstboot --root=/path/to/my/new/root --copy-locale --copy-root-password --hostname=waldi

The tool will be automatically invoked (interactively) now on first boot
if /etc is found unpopulated.

This also creates the infrastructure for generators to be notified via
an environment variable whether they are running on the first boot, or
not.
dhcp-network: ignore IP packets with More Fragments (MF) flag set

We already ignore IP fragments, because we expect that Fragment
offset (FO) field is not set. However first fragment in a fragmented IP
flow will have all zeroes in FO field. We should ignore such packet as
well, thus we need to look at MF flag in the IP header. Checking MF flag
will filter out all except last packet in fragmented flows. Last one
will be ruled out by next check for value of FO.
dhcp-network: make clear that we are ANDing Fragment offset field with mask

Reading BPF assembly written as C macros is inherently difficult. Don't
make it harder than necessary and provide clearer explanation in the
comment.
firstboot: change /etc/shadow access mode to 000

It appears to be customary to remove all access bits from /etc/shadow
including those for the root owner), hence let's do the same.
core: Added support for ERRNO NOTIFY_SOCKET message parsing, and added StatusErrno dbus property along StatusText to allow notification of numeric status condition while degraded service operation or any other special situation.
service: minor modernization