void m_cat(struct mbuf *m, struct mbuf *n)
{
    /*
     * If there's no room, realloc
     */
    if (M_FREEROOM(m) < n->m_len)
        m_inc(m, m->m_len + n->m_len);

    memcpy(m->m_data + m->m_len, n->m_data, n->m_len);
    m->m_len += n->m_len;

    m_free(n);
}
void m_cat(struct mbuf *m, struct mbuf *n)
{
     
    if (M_FREEROOM(m) < n->m_len)
        m_inc(m, m->m_len + n->m_len);

    memcpy(m->m_data + m->m_len, n->m_data, n->m_len);
    m->m_len += n->m_len;

    m_free(n);
}