Force IP addrs, don't pass through host names

When the auto networking plugin assigns sockets it passes through
`local_host` and `media_addr` preset values. The problem is that if
these are long enough or malformed enough SIPp will just crash. So just
always force them to addresses at the inset and avoid yet another SIPp
nightmare...

pysipp/netplug.py

@@ -35,11 +35,13 @@ def pysipp_conf_scen(agents, scen):
     for ua in scen.agents.values():
         copy = scen.prepare_agent(ua)
 
+        ip, port = getsockaddr(ua.local_host)
+
         if not copy.local_host:
-            ua.local_host = host
+            ua.local_host = ip
 
         if not copy.local_port:
-            ua.local_port = getsockaddr(ua.local_host)[1]
+            ua.local_port = port
 
         if not copy.media_addr:
             ua.media_addr = ua.local_host