vxlan bridge mode doesn't handle ovs restart gracefully

[kahou82]

When I use vxlan bridge mode, docker run seems stuck when ovs get restart.

Steps to reproduce:

1. make demo
2. netctl global set --fwd-mode bridge
3. netctl network create -s 10.0.0.0/24 -g 10.0.0.1 -e vxlan -pkt-tag 100 net1
4. docker run -itd --name c1 --net net1 debian /bin/bash
5. restart ovs-switchd
6. docker run -itd --name c2 --net net1 debian /bin/bash

step #6 will stuck