This patch changes the network filtering code to use libvirt's existing
IPv4 and IPv6 address parsers/printers rather than my self-written ones.

I am introducing a new function in network.c that counts the number of
bits in a netmask and ensures that the given address is indeed a netmask,
return -1 on error or values of 0-32 for IPv4 addresses and 0-128 for
IPv6 addresses. I then based the function checking for valid netmask
on invoking this function.

Fix this warning, there is no need to use an intermediate,
different array pointer.
network.c: In function 'getIPv6Addr':
network.c:50: warning: dereferencing type-punned pointer will break strict-aliasing rules
* src/util/network.c: avoid an intermediary pointer cast

* src/util/network.c: getIPv4Addr() got broken when the input
  network address value got converted from network to host byte order

* src/util/network.c: Add htons and ntohs in virSocket(Get|Set)Port

__in6_u.__u6_addr16 is the private name for this struct member,
s6_addr16 is the public one
* src/util/network.c: dont use the private field, but the public one.

* src/util/network.[ch] Add functions for address->text and get/set
  port number
* src/libvirt_private.syms: add new entry points

* src/util/network.c: fix a few typo

* src/util/network.h src/util/network.c: utilities to parse network
  addresses, check netmask and compute ranges