This is a general cleanup of things like code style issues and code structure of the STM32w port to make it more like the rest of Contiki is structured.
Setting UIP_CONF_IPV6 to zero from the make build command line is
something that seems like it should ensure that IPv6 is disabled, but in
fact it actually *enables* IPv6. This seems counter intuitive, so this
patch changes the behavior of the makefiles to handle this case
properly.