Update Net-Ping to CPAN version 2.51

Update Net-Ping to CPAN version 2.51

  [DELTA]

2.51  Mon Oct 17 16:11:03 2016 +0200 (rurban)
       version in cperl since 5.25.2c

       Bugfixes
       - Fixed missing _unpack_sockaddr_in family, which took AF_INET6 for
         a AF_INET addr in t/500_ping_icmp.t and t/500_ping_icmp_ttl.t.
         Use now a proper default.

2.50  Sat Apr 16 11:50:20 2016 +0200 (rurban)
       version in cperl since 5.22.2c

       Features
       - Handle IPv6 addresses and the AF_INET6 family.
       - Added the optional family argument to most methods.
         valid values: 6, "v6", "ip6", "ipv6", AF_INET6
       - new can take now named arguments, a hashref.
       - Added the following named arguments to new:
         gateway host port bind retrans pingstring source_verify econnrefused
         IPV6_USE_MIN_MTU IPV6_RECVPATHMTU IPV6_HOPLIMIT
       - Added a dontfrag option, setting IP_DONTFRAG and on linux
         also IP_MTU_DISCOVER to IP_PMTUDISC_DO. Note that is ignored if
         Socket does not export IP_DONTFRAG.
       - Added the wakeonlan method
       - Improve argument default handling
       - Added missing documentation

       Bugfixes
       - Reapply tos with ping_udp, when the address is changed.
         RT #6706 (Torgny.Hofstedt@sevenlevels.se)
         ditto re-bind to a device.

       Internals
       - $ip is now a hash with {addr, addr_in, family} not the addr_in packed IP.
       - added _resolv replacing inet_aton,
         _pack_sockaddr_in and _unpack_sockaddr_in replacing sockaddr_in,
         _inet_ntoa replacing inet_ntoa
       - Use _isroot helper, with Win32 _IsAdminUser helper.
       - added several new tests (Steve Peters)

2.43  Mon Apr 29 00:23:56 2013 -0300
        version in perl core since 5.19.9
        Bugfixes
        - Handle getprotobyn{ame,umber} not being available
2.42  Sun May 26 19:08:46 2013 -0700
        version in perl core since 5.19.1
        Bugfixes
        - Stabilize tests
       Internals
        - wrap long pod lines