wifi,mozilla: Switch to strings on the stack

Instead of allocating lots of small strings on the heap all the time,
let's put them on the stack to avoid excessive use of memory.

This patch also fixes the accidental breakage of string version of BSSID
from c6a713a5 and
b858035d which broke WiFi-geolocation
completely even though they fixed buffer-overflows.
3 jobs for more-mem-fixes in 7 minutes and 53 seconds (queued for 13 seconds)
Status Job ID Name Coverage
  Test
passed #678814
ubuntu-16.04

00:03:13

passed #678815
ubuntu-18.04

00:02:52

passed #678816
ubuntu-18.04-no-backend

00:05:12