ATH_AGGR_DELIM_SZ
DIV_ROUND_UP(ATH_AGGR_MINPLEN - (_len), ATH_AGGR_DELIM_SZ))
al_delta = ATH_AGGR_DELIM_SZ + fi->framelen;
mindelim = (minlen - frmlen) / ATH_AGGR_DELIM_SZ;