Add default_gateway for l23network call in fuelmenu

l23network::l3:ifconfig added a new parameter default_gateway
which is default to false now in the following commit:
https://github.com/stackforge/fuel-library/commit/c1e3c4e74cf99fe5ccfab21e22da93e90fc9f3a7

Change-Id: I7b46585fbbc2eb1aa58084b194f3663218513968
Closes-Bug: #1389233
Merge "Add default_gateway for l23network call in fuelmenu"