openvswitch: Unify vport error stats handling.

Following patch changes vport->send return type so that vport
layer can do error accounting.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>

diff --cc net/openvswitch/vport-netdev.c
Simple merge

diff --cc net/openvswitch/vport.c
Simple merge

diff --cc net/openvswitch/vport.h
Simple merge