[network] Silence interface checks

Avoid outputting unneeded cruft on the console

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>
[network] Remove erronous use of const, fix potential memory leak

Using const wrongly, removing to make code more readable and sensible.
Also we do not want to leak the wifi service when connection to internet
sharing mode.

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>
[network] More work on getting connman to handle the usb gadget config

Close to working connman usb gadget handling code. Needs work still though.
Keeping disabled for the time being.

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>