Make some DHCP options and host discovery configurable

- Added broadcast option
- Made host discovery from DHCP configurable
- Some code cleanups

Change-Id: I42191c2fd17ef309c73a5382730d708686b835cd
diff --git a/apps/dhcp/app/src/test/resources/dhcp-cfg.json b/apps/dhcp/app/src/test/resources/dhcp-cfg.json
index abc48a8..4971fa7 100644
--- a/apps/dhcp/app/src/test/resources/dhcp-cfg.json
+++ b/apps/dhcp/app/src/test/resources/dhcp-cfg.json
@@ -9,14 +9,14 @@
         "router": "10.0.0.1",
         "domain": "10.0.0.1",
         "ttl": "63",
-        "lease": "300",
+        "lease": 300,
         "renew": "150",
-        "rebind": "200",
+        "rebind": 200,
         "delay": "3",
-        "timeout": "150",
+        "timeout": 150,
         "startip": "10.0.0.110",
         "endip": "10.0.0.130"
       }
     }
   }
-}
\ No newline at end of file
+}