qemu.tests.netperf_udp: extend netperf support in windows guest

bug fix in windows guest.
Support netperf client in windows guest.

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.cfg.virtual_nic_send_buffer: Update netperf related configure.

Signed-off-by: Feng Yang <fyang@redhat.com>
Merge pull request #99 from FengYang/netperf_udp

qemu.tests.netperf_udp: extend netperf support in windows guest