Hotfix against "OTA of large files results in device hangs" (#7458)

Also includes backports from 3.0.0-dev:

• boards: 4dsystems (gen4iod) updates (#7433)
• Free space of overwritten files in LittleFS (#7434)
• Keep client certs when server authentication set (#7464)
• CVE-2020-12638 workaround for WPA downgrade attack (#7486)
• Initialize _ledPin (#7487)
• Correct stack string buffer length (#7488)