Revert "Revert "bond: problem switching from l2 to l3""

This reverts commit 5d0d5494db58422eb528c0f8b39a86ea966505e9.

The csit crash was actually due to the test image missing the patch
https://gerrit.fd.io/r/#/c/17731/

It was a mistake to revert the original patch
https://gerrit.fd.io/r/#/c/15577/

Change-Id: I7fc563981aa13d308d55b25194fee21475ebc57d
Signed-off-by: Steven Luong <sluong@cisco.com>
diff --git a/src/vnet/bonding/device.c b/src/vnet/bonding/device.c
index d333dfc..0ca7f9e 100644
--- a/src/vnet/bonding/device.c
+++ b/src/vnet/bonding/device.c
@@ -104,6 +104,17 @@
 	ethernet_set_rx_redirect (vnm, sif_hw, 1);
       }
     }
+  else if ((bif_hw->l2_if_count == 0) && (l2_if_adjust == -1))
+    {
+      /* Just removed last L2 subinterface on this port */
+      vec_foreach (sw_if_index, bif->slaves)
+      {
+	sif_hw = vnet_get_sup_hw_interface (vnm, *sw_if_index);
+
+	/* Allow ip packets to go directly to ip4-input etc */
+	ethernet_set_rx_redirect (vnm, sif_hw, 0);
+      }
+    }
 
   return 0;
 }