Detect enabling of hairpin mode on vethwe-bridge

Enabled hairpin mode on vethwe-bridge was one of the root causes
for installing looping flows in the fastdp mode.

Also, it confused the weave custom L2 bridge, as the bridge treats
a bounced back packet, e.g. ARP brodcast request, as a local one
(the case for "Captured a packet associated with remote host").

test/705_detect_hairpin_test.sh

@@ -0,0 +1,12 @@
+#! /bin/bash
+
+. ./config.sh
+
+start_suite "Detect hairpin mode"
+
+weave_on $HOST1 launch
+
+assert_raises "run_on $HOST1 sudo ip link set vethwe-bridge type bridge_slave hairpin on"
+assert_raises "docker_on $HOST1 logs weave 2>&1 | grep -q 'Hairpin mode enabled on \"vethwe-bridge\"'"
+
+end_suite