WiFi.SSID() returns a temporary String object. Calling .c_str() on it
returns a pointer to the internal buffer, but the String is destroyed
at the end of the statement - leaving a dangling pointer.
Fix by caching the SSID in a member variable when connection state
changes, and returning a pointer to that stable storage.
Also fix getWiFiStatus() in MyMesh.cpp which was using WiFiState enum
values instead of NetworkState (the interface return type).
Ryan Malloy
91d144901a