Bug 1067677 - Make wifi scanning in FTU more reliable and quicker (r=fcampo)

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Code submitted by Giovanni Charles
Rebased after by Fernando Campo
(see bug's comments for explanation)
Merge pull request #26025 from fcampo/fte-better-wifi-scan

Bug 1067677 - Make wifi scanning in FTU more reliable and quicker (r=fcampo)