ping: Fix protocol selection with NOINET6 kernel.

A missing else caused the correct resolver hint (AF_INET) to be
overwritten with AF_UNSPEC when the kernel supports IPv4 but not
IPv6.

MFC after: 3 days
PR: 277592
Sponsored by: NetApp, Inc.
Sponsored by: Klara, Inc.
Reviewed by: allanjude
Differential Revision: https://reviews.freebsd.org/D44304