Document the behavior of the Outdoor mode when preserve_channels is
enabled.

This reverts commit 4e070312.

The recommendation is not sufficient at this time, so revert it.

See #1898 for further discussion.

many AVM devices do not have RESET/WPS buttons. So use the otherwise unused DECT/PHONE button to boot the device into setup mode.

This patch allows to enter the setup-mode by pressing the phone button
(often labeled as DECT) in addition to WPS and reset button.

This patch is necessary to allow supporting boards without a WPS and reset
button (e.g. AVM FRITZ!Box 7312).

This reverts commit b92e4044.

Committing in this case is unnecessary as that job is already handled by 998-commit
which is in a superior position to commit, as it is run after all relevant changes to
the configuration have been made.

add a missing command to set the special Gluon MAC address of the private WLAN interface to the documentation.

dnsmasq's caching is severly broken and does not handle all answer records
equally. In particular, its cached answers are missing DNSKEY and DS
records, breaking DNSSEC validation on clients.

Remove the cache for now. It may return if dnsmasq is fixed or we switch to
a different resolver.

The 'auto' attribute still allows enabling the interface using ifup, which
is not intended when wired mesh is disabled.

Adding the fact that GLUON_RELEASE is needed with 'make manifest'
if it is used with 'make'.

This fact was mentioned in the v2017.1 release notes but is not (clearly)
mentioned inside other parts of the documentation.

Signed-off-by: Chrissi^ <chris@tinyhost.de>

[Matthias Schiffer: minor rewording]

Adding hints that the next_node name should contain a dot to avoid (mobile) browsers interpreting "nextnode" as searchphrase. Also setting it to an fqdn helps when clients use static dns servers.

gluon-core: dns-cache documentation polish
Now its clear that upstreams severs normally means "community gateways".
* added cacheentries to description
* made upstream server description more general
* description of the A and AAAA-records for next_node added
* mention of Cache not being allocated when not set in site.conf 
* dns-cache doku polish