WifiS3 - Non blocking Wifi connect

[k3ldar]

This PR prevents non blocking connection to wifi, so that normal loop processing can continue whilst waiting for the connection to be established.

Also a potential bug fix in Modem.cpp where MODEM_TIMEOUT was used during begin, effectively ignoring what a user may have set the value to.

Appreciate it's a long shot this getting through, but happy to make adjustments if required.

[CLAassistant]

All committers have signed the CLA.

[JAndrassy]

this platform has two WiFi libraries. please specify WiFiS3 in the title