Fix Windows wrong output

[w6rsty]

Due to the fact that netsh output is based on the system's language settings, simply using "completed successfully" to check the result will not work in other languages

https://github.com/toksdotdev/wifi-rs/blob/c46c05d095710ca9f062efecade698e8feac84a5/src/connectivity/providers/windows.rs#L50-L52

To address this issue while keeping the solution simple, I use the user-provided ssid to match the output of netsh wlan show interfaces

I've also added a check to see if the system is already connected to the specified WLAN