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.
declarations of functions for setting and getting a node ID number, a
functionality that exists on many platforms. Since this functionality
was not considered part of the Contiki core, each platform defined its
own node-id.h file. This commit attempts to clean this up by
collecting the node-id.h into a core/sys/node-id.h file that replaces
the old node-id.h files from the platform directories.
