ovn: Fix the test failures in travis CI.

ovn: Fix the test failures in travis CI.

After the commit [1], below test cases are failing repeatedly in travis CI.

2663: ovn -- 4 HV, 1 LS, 1 LR, packet test with HA distributed router gateway port FAILED (ovn.at:8597)
2664: ovn -- 4 HV, 3 LS, 2 LR, packet test with HA distributed router gateway port FAILED (ovn.at:8844)
2667: ovn -- vlan traffic for external network with distributed router gateway port FAILED (ovn.at:9580)
2691: ovn -- router - check packet length - icmp defrag FAILED (ovn.at:13624)

With the commit [1], ovn-controller sends GARPs for the IPs of the distributed
router ports. The failing tests did not handle the situation if multiple GARPs
are sent. The failures are mostly timing related. This patch fixes these issues.

[1] - d65586b6fa97 ("ovn: Send GARP for router port IPs of a router port connected to bridged logical switch")

Fixes: d65586b6fa97 ("ovn: Send GARP for router port IPs of a router port connected to bridged logical switch")
CC: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Numan Siddique <nusiddiq@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>