conf-parser: distinguish between multiple sections with the same name

Pass on the line on which a section was decleared to the parsers, so they
can distinguish between multiple sections (if they chose to). Currently
no parsers take advantage of this, but a follow-up patch will do that
to distinguish

[Address]
Address=192.168.0.1/24
Label=one

[Address]
Address=192.168.0.2/24
Label=two

from

[Address]
Address=192.168.0.1/24
Label=one
Address=192.168.0.2/24
Label=two
networkd: add support for [Address] sections

This will allow specifying more options per address than the
simple Address= entry in the [Network] section.

Preliminary support for the same functionality for [Route] sections
are added, but not yet hooked up, as more testing is needed.
delete unused variables
shutdown: during final killing spree also send SIGHUP in addition to SIGTERM to deal with shells

This makes shutdown a bit faster if debug-shell.service is enabled.
swap: always track the current real device node of all swap devices, even when not active

This way, we can avoid executing two /bin/swapon jobs to be dispatched
for the same swap device if it is configured for two different paths.

Previously we were just tracking the device nodes of active swap
devices, which would not allow us to recognize the identity of two swap
devices before they are active.

https://bugs.freedesktop.org/show_bug.cgi?id=69835
core: include following set data in dump
service: fix handling of PID file inotify events
bus: properly return errors to client if invalid parameters are passed to built-in methods
core: fix order of parameters in broadcast_signal()
conf-parser: fix memory realloc error

Otherwise there is some memory corruption and undefined behavior,
e.g., in my case systemd-udev was always aborted at the
_cleanup_freep_ around that code blocks.
networkd: use correct printf formatter

uint64_t can be formatted correctly with %ju, rather than casting to
unsigned and potentially losing accuracy.
rtnl: add preliminary support for containers

For now, we only support one container type IFLA_LINKINFO, and we
still lack support for parsing the containers again.
rtnl: add support for IFLA_MASTER
networkd: minor fixes

In particular, store the ifname, though we should only use it carefully, as
it is not guaranteed to be stable. Using it for logging is fine though.
networkd: add bridge support

A bridge is specified in a .netdev file with a section [Bridge]
and at least the entry Name=.

A link may be joined to a bridge if the .network applied to it has
a Bridge= entry giving the name of the bridge in its [Network] section.

We eagerly create all bridges on startup, and links are added to
bridges as soon as they both appear.
core: replace OnFailureIsolate= setting by a more generic OnFailureJobMode= setting and make use of it where applicable
core: add new "flush" job mode to cancel all other jobs when queuing a new job
systemctl: replace the three job mode options by a single --job-mode= option

Also, expose the new "flush" job mode this way.
man: explain the precise syntax and feature set of unit names at the end of the man page, given that it is detail information
nspawn: improve error message when we cannot resolve the root directory argument