enhancement - getter for _persistent

[tablatronix]

_persistent is protected, It would be nice to have a getter for this, in case a library needs to know the users set state etc.

[devyte]

I invite you to implement it, and propose a PR.

[tablatronix]

added PR

[tablatronix]

  Serial.println(WiFi.getPersistent());
  WiFi.persistent(false);
  Serial.println(WiFi.getPersistent());
  WiFi.persistent(true);
  Serial.println(WiFi.getPersistent());