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.

* global: patch created by running:
for f in $(git ls-files '*.[ch]') ; do
    cppi $f > $f.t && mv $f.t $f
done

MinGW's ld gives an error when trying to export undefined symbols.

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