autotest: wifi: Set WiFi Address for local servers

If we are in a "local server" configuration, the IP address of the
server on the WiFi is determined by the server itself, not by
external configuration.  Test for this configuration.

BUG=chromium-os:25908
TEST=network_WiFiMatFunc/060Perf24HT20

Change-Id: I986571f398673e8166eca67651eec6e02b226217
Reviewed-on: https://gerrit.chromium.org/gerrit/38494
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
diff --git a/server/site_linux_router.py b/server/site_linux_router.py
index 7cb930b..5baebbf 100644
--- a/server/site_linux_router.py
+++ b/server/site_linux_router.py
@@ -374,14 +374,16 @@
         self.station['interface'] = interface
 
 
+    def local_server_address(self, index):
+        return '%d.%d.%d.%d' % (192, 168, index, 254)
+
     def start_local_server(self, interface):
         logging.info("Starting up local server...")
 
         if len(self.local_servers) >= 256:
             raise error.TestFail('Exhausted available local servers')
 
-        netblock = '%d.%d.%d.%d/24' % \
-            (192, 168, len(self.local_servers), 254)
+        netblock = '%s/24' % self.local_server_address(len(self.local_servers))
 
         params = {}
         params['netblock'] = netblock