Wireless bitrate and quality are not updated

When starting i3 the wireless `%bitrate` and `%quality` are fetched once but will not be updated afterwards.

`iw` shows the constant changes in bitrate and signal quality that i3status is missing.

Running i3status 2.10, Linux 4.3.3 and iwlwifi.

Start by tracing how i3status obtains the wireless %bitrate and %quality values and compare that behavior with the changing values reported by iw. Confirm the values are refreshed after i3 starts, then verify that the status output reflects subsequent bitrate and signal-quality changes.

Written by the indexing model from the issue text.