VGE_RX_BUF_ALIGN
m_adj(m, VGE_RX_BUF_ALIGN);
m->m_len = MCLBYTES - VGE_RX_BUF_ALIGN;
m->m_len = total_len % (MCLBYTES - VGE_RX_BUF_ALIGN);
VGE_RX_BUF_ALIGN, 0, /* algnmnt, boundary */