sd-bus: rework ELF error mapping table magic

The ELF magic cannot work for consumers of our shard library, since they
are in a different module. Hence make all the ELF magic private, and
instead introduce a public function to register additional static
mapping table.
update TODO
bus: StartTransientUnit can have aux unit
timer: timer can be a transient unit
networkd: update manpage for optional Gateway=

Following commit 59580681f5f.
Check return value from reading name_assign_type attr

This file won't exist on kernels earlier than 3.17.
udev: link-config - simplify net-match
networkd: route - ignore unknown address family
sd-rtnl: fix bogus warning about dropping 20 bytes from multi-part messages

Nothing was being dropped, we just failed to account for the NLMSG_DONE.
networkd: link - typo
journal: Fix navigating backwards missing entries

With DIRECTION_UP (i.e. navigating backwards) in generic_array_bisect() when the
needle was found as the last item in the array, it wasn't actually processed as
match, resulting in entries being missed.

https://bugs.freedesktop.org/show_bug.cgi?id=86855
networkd: manager - enumerate addresses globally, rather than per-link

The kernel always returns all addresses, rather than only for the given link, so let's only enumerate once.
load-fragment: remove wrong ifdef guard

config_parse_warn_compat is now always used for removed options.

https://bugs.freedesktop.org/show_bug.cgi?id=87125
bus-proxy: fix compat with autostarted services
update TODO
sd-bus: catch up with current kdbus, don't do matches on kdbus monitor connections
update TODO
sd-rtnl: fix size check in sd_rtnl_message_append_string()
nspawn: make sure macvlan MAC addresses are stable

https://bugs.freedesktop.org/show_bug.cgi?id=85527
update TODO