Load SMI MIB module

If tcpdump is built with libsmi support, "-m module" option can be used to load MIB module (code is here):

int
nd_load_smi_module(const char *module, char *errbuf, size_t errbuf_size)
{
#ifdef USE_LIBSMI
    if (smiLoadModule(module) == 0) {
        nd_snprintf(errbuf, errbuf_size, "could not load MIB module %s",
            module);
        return (-1);
    }
    nd_smi_module_loaded = 1;
    return (0);
#else
    nd_snprintf(errbuf, errbuf_size, "MIB module %s not loaded: no libsmi support",
        module);
    return (-1);
#endif
}