dockershim/network: add dcbw to OWNERS as an approver

I've been involved with the kubelet network code, including most
of this code, for a couple years and contributed a good number
of PRs for these directories. I've also been a SIG Network
co-lead for couple years.

I've also been on the CNI maintainers team for a couple years.

pkg/kubelet/dockershim/network/OWNERS

@@ -3,6 +3,7 @@ approvers:
 - dchen1107
 - matchstick
 - freehan
+- dcbw
 reviewers:
 - sig-network-reviewers