Cleanup and fix the network code.

Cleanup and fix the network code.

- introduce network_free() to properly free a network struct including
  the possible rtlabel reference.
- change expand_networks() and the reload code to not only expand the
  main network config but also the network configs inside L3VPN sections.
- adjust reload logic to properly match any kind of network struct.
  Up until now rtlabel and priority network statememnts were not correctly
  reloaded.
OK tb@