[Regression] FlowMod delete with cookie but without match fields is matching incorrectly

[viniarck]

Issue

If you send a FlowMod delete with cookie set but without any match fields, which is exactly the kind of match that mef_eline sends when removing EVCs, it was matching more entries since I messed up an order of an early return on this PR #25.

How to reproduce

• Run mininet:
  sudo mn -c && sudo mn --controller=remote,ip=127.0.0.1,port=6653 --switch=ovsk,protocols=OpenFlow13 --topo=linear,5

• Start kytos, with mef_eline and of_lldp, installed as well:
  kytosd -f -E

• Double check the current existing installed flows:

mininet> sh ovs-ofctl dump-flows s1 -O OpenFlow13 --rsort=priority
 cookie=0x0, duration=64.805s, table=0, n_packets=20, n_bytes=840, send_flow_rem priority=1000,dl_vlan=3799,dl_type=0x88cc actions=CONTROLLER:65535
mininet>

• Request an EVC EPL on mef_eline with this payload:

{
    "name": "evc1",
    "dynamic_backup_path": true,
    "uni_a": {
        "interface_id": "00:00:00:00:00:00:00:01:1"
    },
    "uni_z": {
       "interface_id": "00:00:00:00:00:00:00:02:1"
    }
}

• Notice the flows will be installed:

mininet> sh ovs-ofctl dump-flows s1 -O OpenFlow13 --rsort=priority
 cookie=0xaa67c174903df944, duration=5.006s, table=0, n_packets=0, n_bytes=0, send_flow_rem in_port="s1-eth1" actions=push_vlan:0x88a8,set_field:4416->vlan_vid,output:"s1-eth2"
 cookie=0xaa67c174903df944, duration=5.003s, table=0, n_packets=0, n_bytes=0, send_flow_rem in_port="s1-eth2",dl_vlan=320 actions=pop_vlan,output:"s1-eth1"
 cookie=0x0, duration=132.803s, table=0, n_packets=42, n_bytes=1764, send_flow_rem priority=1000,dl_vlan=3799,dl_type=0x88cc actions=CONTROLLER:65535
mininet>

• After some time, when the consistency check again, it'll remove the of_lldp, dl_vlan=3799,dl_type=0x88cc actions=CONTROLLER:65535 entry, since mef_eline under the hood will send a delete, which our matching function is incorrectly matching incorrectly and deleting entries that aren't supposed to (this was an issue of a wrong order of an early return in the code):

mininet> sh ovs-ofctl dump-flows s1 -O OpenFlow13 --rsort=priority
 cookie=0xaa67c174903df944, duration=59.788s, table=0, n_packets=0, n_bytes=0, send_flow_rem in_port="s1-eth1" actions=push_vlan:0x88a8,set_field:4416->vlan_vid,output:"s1-eth2"
 cookie=0xaa67c174903df944, duration=59.785s, table=0, n_packets=0, n_bytes=0, send_flow_rem in_port="s1-eth2",dl_vlan=320 actions=pop_vlan,output:"s1-eth1"
mininet>