wifinina: add mutex to prevent communication race problems

[deadprogram]

This PR adds a mutex to the WifiNINA driver to prevent communication race problems when multiple goroutines try to access adaptor at the same time.

[ysoldak]

Why don’t put mutex on all public methods? Basically any “concurrent” access to wifinina upsets communication. Like one goroutune does networking, another does RGB leds…

[deadprogram]

@ysoldak I tried to only use the mutex where it seemed absolutely needed. Are there any specific functions you think I should cover that I missed, or is this more of a general comment?

[ysoldak]

@deadprogram general comment, yes.

[deadprogram]

That being the case, I will merge this and then further improvements can continue from there. Thanks @ysoldak