localectl,man: make it obvious that set-*-keymaps sets both keymaps

https://bugs.freedesktop.org/show_bug.cgi?id=85411
TODO: update

Drop resolved kdbus issues.
bus: fix memfd-cache regarding memfd offsets

We must restore part->mmap_begin when poping memfds from the memfd-cache.
We rely on the memfds to be unsealed, so we can be sure that we own the
whole FD. Therefore, simply set part->mmap_begin to the same as
part->data.

This fixes test-bus-kernel-benchmark.
bus: zero cmd_free before passing to ioctl

Make sure the whole cmd_free object is zeroed before passing it into the
kernel. This makes valgrind happy and makes us future proof.
bus: sync with kdbus.git

Sync up with recent kdbus changed:
 * several ioctls gained .size and .items members (but still unused)
 * CMD_SEND gained its own ioctl structure
 * several members of kdbus_msg were dropped as they were only used during
   SEND, not during RECV etc.
 * CMD_RECV and CMD_SEND now share a kdbus_reply member which contains the
   offset and size of the returned message.
libsystemd: add sd-hwdb library

This is libudev-hwdb, but decoupled from libudev and in the libsystemd style.

The core code is unchanged, apart from the following minor changes:

 - hwdb.bin located in /**/systemd/hwdb/ take preference over the ones located
   in /**/udev/
 - properties are stored internally in an OrderedHashmap, rather than a
   linked list.
 - a new API call allows individual properties to be queried directly, rather
   than iterating over them all
 - the iteration over properties have been moved inside the library, rather than
   exposing a list directly
 - the unused 'flags' parameter was dropped
libudev: make libudev-hwdb a wrapper around sd-hwdb
tests: udev - assume /etc/machine-id rather than /etc/hosts

On todays machines /etc/hosts is not mandatory. /etc/machine-id is though, so let's rely on that instead.

This makes the udev tests pass again for me.
sd-dhcp-client: log if we fail to set up lease timers
update TODO
build-sys: fix user unit m4 logic
networkd/resolved: correct spacing near eol in code comments
sd-bus: correct spacing near eol in code comments
journald: correct spacing near eol code comments
shared: correct spacing near eol in code comments
core: correct spacing near eol in code comments
treewide: correct spacing near eol in code comments
tree-wide: use our memset() macros instead of memset() itself
bus: sync with kdbus.git

Changes:
 * bloom parameters are returned in an offset via HELLO
 * FREE now takes items just like any other ioctl
test-unit-name: add tests for %f