BFE_MAXTXSEGS
bus_dma_segment_t txsegs[BFE_MAXTXSEGS];
m = m_collapse(*m_head, M_NOWAIT, BFE_MAXTXSEGS);
MCLBYTES * BFE_MAXTXSEGS, /* maxsize */
BFE_MAXTXSEGS, /* nsegments */