Move UDP listen inside try block

src/allmydata/util/iputil.py

@@ -6,6 +6,7 @@ from sys import platform
 # from Twisted
 from twisted.internet import defer, threads, reactor
 from twisted.internet.protocol import DatagramProtocol
+from twisted.internet.error import CannotListenError
 from twisted.python.procutils import which
 from twisted.python import log
 
@@ -125,16 +126,17 @@ def get_local_ip_for(target):
         # avoid this DNS lookup. This also makes node startup fractionally
         # faster.
         return None
+    
+    try:
         udpprot = DatagramProtocol()
         port = reactor.listenUDP(0, udpprot)
-    try:
         udpprot.transport.connect(target_ipaddr, 7)
         localip = udpprot.transport.getHost().host
-    except socket.error:
-        # no route to that host
-        localip = None
         d = port.stopListening()
         d.addErrback(log.err)
+    except (socket.error, CannotListenError):
+        # no route to that host
+        localip = None
     return localip