Invalid ovs-agent test case - test_fdb_add_flows

setup_tunnel_port is an attribute of self.agent and not self.agent.tun_br.
This patch fixes the testcase accordingly.

Closes-Bug: #1284265
Change-Id: I70582e477bb53de6482e32d5913c0864c5d910cc
Merge "Invalid ovs-agent test case - test_fdb_add_flows"