o Add "npkts_resized" stat, to track number of packets passed on
for resizing;

o implement 3 more methods into rtpp_stats object, which makes it
actually usable:
 - getidxbyname()
 - updatebyidx()
 - getlvalbyname().
Implement all npkts_xxx counters (npkts_rcvd, npkts_played,
npkts_relayed and npkts_discard). Use first 3 to replace
old cf->packets_in / cf->packets_out in the "info"
command. More advanced "stats" command is coming.