isConnectedToNetwork() always returned false on ARCH_PORTDUINO
because none of HAS_WIFI, HAS_ETHERNET, or USE_WS5500 are defined
for Linux native builds. This caused wantsLink() to always return
false, preventing the MQTT thread from ever connecting at boot.
Fix: return true for ARCH_PORTDUINO since Linux always has network
access available.
Co-authored-by: Jonathan Bennett <jbennett@incomsystems.biz>
