Enable users of ip to specify the times for rtt, rttvar and rto_min
in human-friendly terms a la "tc" while maintaining backwards
compatability with the previous "raw" mechanism.  Builds upon
David Miller's uncommited patch to set rto_min.
Signed-off-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>