The below mentioned commit introduced a regression, that the "wifi"
section of the request type "neighbours" was empty:

    ~# gluon-neighbour-info -d ::1 -r neighbours | ffh_pretty_json
    {
      "wifi": [
      ],
      ...
    }

After this commit, the section (correctly) looks like this:

    root@UFU-FWH-A272-Tresckowstr-GemR-vorne:~# gluon-neighbour-info -d ::1 -r neighbours | ffh_pretty_json
    {
      "wifi": {
        "ca:38:7e:42:5f:21": {
          "neighbours": {
            "fe:9f:4d:01:ea:e1": {
              "noise": -102,
              "inactive": 50,
              "signal": -84
            },
            "fe:df:b9:84:37:51": {
              "noise": -102,
              "inactive": 20,
              "signal": -73
            }
          }
        }
      },
      ...
    }

The issue was due to the fact, that the iteration over the (mesh) wifi interfaces
was broken. The code was assuming, that the section

    config interface 'mesh_radio0'
            option proto 'gluon_mesh'

in /etc/config/network contains an option "ifname", which it does not.
The ifname property is only stored in the corresponding section in
/etc/config/wireless:

    config wifi-iface 'mesh_radio0'
            option ifname 'mesh0'
            option network 'mesh_radio0'
            option mode 'mesh'
            ...

Therefore, we now iterate over wifi-ifaces in /etc/config/wireless, that
have the mode 'mesh' instead. This resolves the issue.

Fixes 0f1fa243

Fixes warnings about implicit pointer-to-int and int-to-pointer casts.

Fixes: 59a4cd63 ("gluon-respondd: expose OWE clients in nodeinfo")

Closes #1974

Situation:
==========

$ ls -l /lib/gluon/domains/lindennord.json
lrwxrwxrwx    1 root     root            10 Jan  6 03:42 /lib/gluon/domains/lindennord.json -> dom17.json

Before:
=======

$ gluon-neighbour-info -d ::1 -p 1001 -r nodeinfo -c 1
{
   "node_id": "525400123456",
   "system": {
     "domain_code": "lindennord",
     "site_code": "ffh"
   },
...
}

After:
======

$ gluon-neighbour-info -d ::1 -p 1001 -r nodeinfo -c 1
{
   "node_id": "525400123456",
   "system": {
     "primary_domain_code": "dom17",
     "domain_code": "lindennord",
     "site_code": "ffh"
   },
...
}

Provide the number of OWE stations in addition to the number of all
connected wireless clients.

In addition this PR contains:
- split of gluon-respondd provider into multiple source files
- minor additional cleanups in gluon-mesh-babel respondd provider
  (untested, as the babel respondd provider already doesn't compile prior
  to these changes...)

This commit adds information about:
- how cpu time is spent since boot in jiffies (1/100*sek) (cpu)
    - the value is summed for all cores, so in 10 seconds the
      summed values will increase by 4000, if the cpu has
      4 cores
- context switches since boot (ctxt)
- interrupt counters since boot (intr, softirq)
- forks since boot (processes)

    { "stat": {
       "cpu": {
         "user": 219403,
         "nice": 1714,
         "system": 75159,
         "idle": 2727739,
         "iowait": 2943,
         "irq": 0,
         "softirq": 571
       },
       "intr": 8426340,
       "ctxt": 50992590,
       "processes": 10549,
       "softirq": 5161884
    } }

[Matthias Schiffer: rebase]

Fixes #414

Most doubles that are delivered via respondd have limited input
precision, but are converted with up to 17 digits of precision. That can
cause ugly blowups like 0.2800000000000001 in the output, which is
avoided by specifying better format strings (like "%.2f" in most cases).

gluon-announced and gluon-announce are merged to gluon-respondd.