Allows a raspberry pi to, for example, share a connection using a Cellular dongle with Soracom SIM card

1. In order to share a Cellular connection, you have the following two options:
   1. Share over Ethernet, simply add the ETH_SHARE=1 variable in resin config and your Ethernet based sharing configuration will be added
   2. Share over WiFi, add WIFI_NETWORK= and WIFI_PASSWORD= variable in resin config and your WiFi based sharing configuration will be added

Once a WiFi or Ethernet based connection sharing has been added, it will not be updated