dev: Add a missing parameter to the EtherTap device.

There needs to be a SlavePort called "tap" for the ethertap device to be
able to connect to the gem5 network successfully.

Change-Id: I1ad81219f612fd1ec278c6148af728d20bc916da
Reviewed-on: https://gem5-review.googlesource.com/3580
Reviewed-by: Nathan Binkert <nate@binkert.org>
Maintainer: Nathan Binkert <nate@binkert.org>

src/dev/net/Ethernet.py

@@ -101,6 +101,7 @@ class EtherTap(EtherObject):
     bufsz = Param.Int(10000, "tap buffer size")
     dump = Param.EtherDump(NULL, "dump object")
     port = Param.UInt16(3500, "tap port")
+    tap = SlavePort("Ethernet interface")
 
 class EtherDump(SimObject):
     type = 'EtherDump'