rescue: include ping iff at least one of INET & INET6 is enabled

Ping does not build (and serves no purpose) if neither is enabled
(i.e., building WITHOUT_INET and WITHOUT_INET6).

This is equvalent to a4ef9e58bc0c but for rescue/.

PR: 260082
Fixes: a4ef9e58bc0c ("sbin: build ping if at least one of...")
Sponsored by: The FreeBSD Foundation