Wi-Fi sensor improvements

[anyuta1166]

Summary

This request addresses 2 issues at once, because they are interconnected:

1. Using wifiManager.scanResults to get signal strength is very unreliable. I often see "-1" on some devices even if Wi-Fi is connected. Use conInfo.rssi for a reliable result.

Also, wifiManager.scanResults is not available if Location is disabled on a device, but conInfo.rssi is available in such case.

2. There is an issue on devices running Android 10+ (tested on various Android 10 and Android 11 devices). If Wi-Fi is connected, but Location is disabled on a device, getNetworkId() returns -1 and Home Assistant app thinks that we are not connected. But some information - IP address, link speed, frequency, signal strength (via getRssi()) is actually still available. If NetworkId == -1, we can additionally check LinkSpeed to determine that we are connected and provide IP address, link speed, frequency and signal strength.

Please note that if Location is disabled on a device, wifiManager.scanResults is not available, but conInfo.rssi is available, that's why I've merged this into one commit.

Screenshots

Link to pull request in Documentation repository

Documentation: home-assistant/companion.home-assistant#

Any other notes

[dshokouhi]

Looks good to me, didn't realize we were hitting an odd issue like that. Thanks for the PR.