ping: The -C option is also supported for IPv6.

MFC after: 3 days
Sponsored by: Klara, Inc.
Sponsored by: NetApp, Inc.
Reviewed by: rscheff, allanjude
Differential Revision: https://reviews.freebsd.org/D41881

(cherry picked from commit a2d1360142f609485c9301df08cc99140743ef2b)