Revise netperf's avg_update

tpkt_per_exit 14=6/12,rpkt_per_irq 15=5/13 according
to following columns.

2               3       4               5       6
throughput  CPU     thr_per_CPU     rx_pkts tx_pkts
7       8       9       10      11      12      13
rx_byts tx_byts     re_pkts rx_intr tx_intr io_exit irq_inj
14             15
tpkt_per_exit rpkt_per_irq

Signed-off-by: wenli <wenli@redhat.com>
Merge pull request #783 from WenliQuan/netperf

Revise netperf's avg_update