Convert all calls to inet_ntoa() to inet_ntop() in preparation for
later IPv6 changes.
Add parameter handling for a family parameter.  This is the start
of IPv6 support. For now...
- ipv4 is the default
- the parameter must be either "ipv4" or "ipv6" or croak
- if it is "ipv6", TOS and TTL are undef'd and warnings delivered
  if either are set.

I am ashamed to admit no new tests have been added for this yet.
Merge branch 'ipv6' of https://github.com/smpeters/net-ping into ipv6

Conflicts:
	lib/Net/Ping.pm