NMIPAddr contains an unnamed union. We have to either explicitly
initialize one field, or omit it.

    ../shared/nm-utils/nm-shared-utils.c:38:36: error: suggest braces around initialization of subobject [-Werror,-Wmissing-braces]
    const NMIPAddr nm_ip_addr_zero = { 0 };
                                       ^
                                       {}