Stop scanning after errors

When scan fails for 3 times, we show a
failure toast and continue to scan.
In one case this caused infinite toasts,
until the user stopped wifi.

Its not clear what can cause this kind of
a state since wifi disable broadcast should
stop the scans. This fix will stop scans
after 3 continuous failures. Any wifi state
change will restart scan.

Bug: 2601937
Change-Id: I68733394cb3c9b76ffb15f7579e7af6c1f54d39c