Proper handling of network configuration while creating jail in UI

When we are creating a plugin, we are seeing 2 issues:

1) On basic plugin creation form, vnet is enabled by default but the interfaces being shown are not vnetX like they are shown when user clicks on advanced section. We should correct this behavior.

2) On advanced plugin creation form, if a user does not select an interface, UI sends "|192.168.0.23/24" to the middleware for ip4_addr value which is also not correct. If no interface is selected, it should send "192.168.0.23/24".