wifi: Only refresh location on BSS list changes

If BSS list hasn't changed since the last location refresh, not much point
in refreshing location and sending redundant query to MLS.

Fixes #100.
3 jobs for dont-spam-mls in 6 minutes and 2 seconds (queued for 2 minutes and 32 seconds)
Status Job ID Name Coverage
  Test
passed #72363
ubuntu-16.04

00:03:36

passed #72364
ubuntu-17.10

00:02:40

passed #72365
ubuntu-18.04

00:02:11