NFS_SDRTT
timeo = NFS_SRTT(req) + NFS_SDRTT(req);
NFS_SRTT(req), NFS_SDRTT(req),
if (d < NFS_SDRTT(rep))
n = ((NFS_SDRTT(rep) * 15) + d) >> 4;
n = ((NFS_SDRTT(rep) * 3) + d) >> 2;
NFS_SDRTT(rep) = n;