This allows to reach the node in setup mode over the same link-local IPv6
address as br-client uses during normal operation.

OpenWrt doesn't set the regdom unless a WLAN device is started. Explicitly set
the regdom in the setup mode to get the correct list of allowed txpower entries
in the planned LuCI module.

This seems to mitigate weird bridge forwarding issues.

This will require site.mk to explicitly pull in the gluon-setup-mode and
gluon-config-mode-core packages.

This also adds an extended query protocol and deflate compression.

Having two POT files will only cause confusion.

In Bremen it has been noted that a prefix may lead people to believe it
has to stay there and thus naming their nodes "ffhb-*", which is not
what the community wants (see FreifunkBremen/gluon-site-ffhb#1).

However, an empty prefix lead to the connecting hyphen still being
inserted. This commit thus makes the hyphen part of the configured
prefix and allows the prefix to be missing from the `site.conf`.