Add Network class

* Network class provides the network object and the function to verify
  that requested client is in the same network.

  The network address is stored in the IPStorage (custom define type)
  which is the union of struct in_addr and struct in6_addr, therefore,
  the network object could store IPv4 or IPv6 network, only one family
  per object.

Signed-off-by: Neutron Soutmun <neo.neutron@gmail.com>