This is related to bug NETVIRT-989.
https://jira.opendaylight.org/browse/NETVIRT-989

Same steps to recreate as above bug.

1. create network
2. create subnet
3. from ODL cli, do vlan:show. Notice new interface for subnet.
4. Delete subnet
5. Observe that interface is not deleted.

In this case, the Interface is not deleted when the subnet is deleted. As a result, we have an Interface leak.

Here is a sample output from my testing. Notice that most of the entries have N/A. This is because vlan:show gets interface from local cache, which is stale because Interface was not deleted.

opendaylight-user@root>vlan:show
Name
Dpn PortName Vlan-Id
Tag PortNo AdmState OpState
Description
--------------------------------------------------------------------------------
ea30f22a-fcb1-41c5-9e90-dbcde3ee65a4
185254290215608 tapea30f22a-fc 0
1 1 ENABLED UP
null

efcff074-e07f-41cc-bba8-b25bf19f38bd
N/A N/A 0
N/A N/A N/A N/A
null

cfe1bf28-5536-4a87-9c75-857002655196
N/A N/A 0
N/A N/A N/A N/A
null

2d36a58d-8fc6-4f6a-ad50-0868b3079452
185254290215608 tap2d36a58d-8f 0
4 13 ENABLED UP
null

9368c800-fe11-4bed-a6ea-15e9115cb437
N/A N/A 0
N/A N/A N/A N/A
null

a75802b1-c45a-4567-a862-05791ca6e0d6
N/A N/A 0
N/A N/A N/A N/A
null

c62c6cb6-67dc-4bd7-a937-e1bbb8a16651
N/A N/A 0
N/A N/A N/A N/A
null

With this fix, interface is now deleted when subnet is deleted.