coova-chilli: add network option

fix #1221

Signed-off-by: Jaehoon You <teslamint@gmail.com>

net/coova-chilli/files/chilli.config

@@ -9,6 +9,9 @@ config chilli
     # name of TUN device name. required.
     option tundev 'tun0'
 
+    # name of network interface
+    option network ''
+
     # Include this flag if process is to run in the foreground
     #option fg