Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Add descriptions to most of the rc scripts. Those are mostly taken from their
daemon's manpage and probably improved.
- Consistently use "filesystem" not "file system".

Approved by: bapt, brueffer
Differential Revision: D452

Remove trailing white space. No functional changes.

With uart(4) default, change /dev/cuad# to /dev/cuau# and
sio# to uart# so that out-of-the-box FreeBSD is consistent.

As previously discussed, add the svn:executable property to all scripts

Use $required_modules wherever suitable. Use load_kld() in special
cases. So we get rid of quite a few lines of duplicated code.

Eliminate global symbols starting with an underscore from rc.d
scripts, except for mdconfig* and jail. Such symbols are reserved
for the rc.subr internals. Most scripts can be fixed by just
declaring _foo symbols as local: few scripts actually need them to
be global.

Discussed with: dougb in freebsd-rc

Start integrating Bluetooth into rc.d system.

Introduce /etc/rc.d/bluetooth script to start/stop Bluetooth devices. It
will be called from devd(8) in response to device arrival/departure events.
It is also possible to call it by hand to start/stop particular device
without unplugging it.

Introduce generic way to set configuration parameters for Bluetooth devices.
By default /etc/rc.d/bluetooth script has hardwired defaults compatible
with old rc.bluetooth from /usr/share/netgraph/bluetooth/examples. These
can be overridden using /etc/defaults/bluetooth.device.conf file (system
wide defaults). Finally, there could be another device specific override
file located in /etc/bluetooth/$device.conf (where $device is ubt0, btccc0
etc.)

The list of configuration parameters and their meaning described in the
/etc/defaults/bluetooth.device.conf file. Even though Bluetooth device
configuration files are not shell scripts, they must follow basic sh(1) syntax.

The bluetooth.device.conf(5) and handbook update will follow shortly.

Inspired by: Panagiotis Astithas ( past at ebs dot gr )
Reviewed by: brooks, yar
MFC after: 1 week