Reduce netperf runtime from netperf start overhead

Fristly according strategy, the largest timeout_netperf_start
should be int(l) * 0.5, if netperf thread start at once, it
will still need int(l) * 0.5 time waste, that's overhead does
not needed.

Signed-off-by: Wenli Quan <wquan@redhat.com>
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 Quan <wquan@redhat.com>