dhcp-network: don't pass ifindex to bind_udp_socket

UDP sockets can anyway not be bound to specific netdev's. The packages would have to be filtered
when received instead.
sd-dhcp: network - set TOS on outgoing packets

This should improve performance on busy wireless networks and the
like. Inspired by a similar change in dnsmasq.
sd-dhcp: network - don't leak sockets on failure

Also some general cleanups
sd-dhcp-client: use asynchronous_close()

close() is a blocking call, which may slow things down measurably when running many dhcp
clients in the same single-threaded main loop. Let's just use the asynchronous version
instead to avoid the problem.
doc: use non-contracted forms in written documents
doc: typographical fine tuning
doc: adhere to XML syntax
timesyncd: shorten log message
sd-network: expose both admin and operational state directly

Also add a call to check if a link is loopback, as this should commonly be ignored.
networkd: link - always maintain link operstate regardless of admin state
networkd-wait-online: rely purely on sd-network events and drop rtnl hooks
po: add Greek translation

https://bugs.freedesktop.org/show_bug.cgi?id=78064
backlight: handle saved brightness exceeding max brightness

If too high a brightness value has been saved (e.g. due to kernel
mechanism changing from one kernel version to another, or booting the
userspace on another system), the brightness update fails and the
process exits.

Clamp saved brightness between the policy minimum introduced in

commit 7b909d7407965c03caaba30daae7aee113627a83
Author: Josh Triplett <josh@joshtriplett.org>
Date:   Tue Mar 11 21:16:33 2014 -0700

    backlight: Avoid restoring brightness to an unreadably dim level

and the absolute maximum.

https://bugs.freedesktop.org/show_bug.cgi?id=78200
doc: corrections to words and forms

This patch exchange words which are inappropriate for a situation,
deletes duplicated words, and adds particles where needed.
doc: comma placement corrections and word order

Set commas where there should be some.
Some improvements to word order.
doc: write out stdin/stdout file descriptors

"When refering to code, STDOUT/STDOUT/STDERR are replaced with
stdin/stdout/stderr, and in other places they are replaced with
normal phrases like standard output, etc."

Addendum to commit v209~127.
doc: balance C indirections in function prototypes

Shift the asterisks in the documentation's prototypes such that they
are consistent among each other. Use the right side to match what is
used in source code.

Addendum to commit v209~82.
core: check the right variable for failed open()
networkd: link - operstate is an enum, not a bitmask
networkd-wait-online: fix false positives when checking if a link is managed by networkd