Fix multiple issues with the wireless information reported by i3status for
- Instead of hoping that the currently associated AP will show up as
the first AP in the list of scan results, fetch the BSSID of the
currently associated AP and use that to fetch station info for the
AP. This provides more frequently updated signal strength
information than scan results and reliably provides information when
multiple APs are in range.
- Do not treat the RSSI value as a raw signal value in dBm. Instead, use
the same formula as ifconfig(8) to compute a signal value.
- Do not report the beacon interval value as a signal quality level.
Reviewed by: bapt
Differential Revision: https://reviews.freebsd.org/D3369