host_tracker doesn't raise events when it learns IP addresses

[nemethf]

If host_tracker receives a packet_in from an unknown host, it raises an event without the host's IP address. The packet_in handler will eventually call updateIPInfo, but that method won't raise a new event. If (dpid,inport,packet.src) never changes, host_tracker listeners will never learn the host's IP address.

I don't think this is a really serious issue because other pox components don't seem to need IP addresses, but external modules (like the one i'm currently writing) might like to use this information.

The correct fix is probably more complex, but here is a one-line-long workaround:

diff --git a/pox/host_tracker/host_tracker.py b/pox/host_tracker/host_tracker.py
index f7fd60c..87dad77 100644
--- a/pox/host_tracker/host_tracker.py
+++ b/pox/host_tracker/host_tracker.py
@@ -309,6 +309,7 @@ class host_tracker (EventMixin):
       ipEntry = IpEntry(hasARP)
       macEntry.ipAddrs[pckt_srcip] = ipEntry
       log.info("Learned %s got IP %s", str(macEntry), str(pckt_srcip) )
+      self.raiseEventNoErrors(HostEvent, macEntry, move=True)
     if hasARP:
       ipEntry.pings.received()

(I think this issue is independent of #125)