Ensure receive_cb and utcp structures have been properly initialized after setting...

[meshlink] / .gitmodules

[submodule "avahi"]
        path = avahi
        url = git@chicago.everbase.net:meshlink/avahi-noptr.git
        branch = noptr
[submodule "src/utcp"]
        path = src/utcp
        url = git://meshlink.io/utcp