round_blksz
blksz = round_blksz(bufsz >> blkcnt, bps, max);
sblksz = round_blksz(blksz, bs->align, maxsize);
hblksz = round_blksz(sndbuf_xbytes(sblksz, bs, b),
hblksz = round_blksz(b->maxsize >> 1, b->align,
nsblksz = round_blksz(