Search in /sys/class/net for network devices

When using /sys/devices/net/virtual to search for tap devices, not all
devices are listed there (i.e. when using Xen).
Also according to the Linux kernel documentation (see
ABI/testing/sysfs-devices), /sys/class should be used
instead of /sys/devices.

Change-Id: I9b4981332b66b6d3f9c36511c81432d3e7644bdd
Closes-Bug: #1419754

neutron/plugins/linuxbridge/agent/linuxbridge_neutron_agent.py

@@ -52,7 +52,9 @@ from neutron.plugins.linuxbridge.common import constants as lconst
 LOG = logging.getLogger(__name__)
 
 BRIDGE_NAME_PREFIX = "brq"
-BRIDGE_FS = "/sys/devices/virtual/net/"
+# NOTE(toabctl): Don't use /sys/devices/virtual/net here because not all tap
+# devices are listed here (i.e. when using Xen)
+BRIDGE_FS = "/sys/class/net/"
 BRIDGE_NAME_PLACEHOLDER = "bridge_name"
 BRIDGE_INTERFACES_FS = BRIDGE_FS + BRIDGE_NAME_PLACEHOLDER + "/brif/"
 DEVICE_NAME_PLACEHOLDER = "device_name"

neutron/tests/unit/linuxbridge/test_lb_neutron_agent.py

@@ -447,7 +447,7 @@ class TestLinuxBridgeManager(base.BaseTestCase):
             exists_fn.return_value = True
             self.assertTrue(self.lbm.is_device_on_bridge("tap1"))
             exists_fn.assert_called_with(
-                "/sys/devices/virtual/net/tap1/brport"
+                "/sys/class/net/tap1/brport"
             )
 
     def test_get_interface_details(self):