util: Avoid overflow in GetNameByINet

We copy the results of gethostbyaddr into a fixed length buffer
without checking whether they fit. Add a length check, and use
strlcpy to do the copy to make sure we can't overflow.

Caught by coverity (#985912, #985872)

Change-Id: I1e8f0fbb2577199c25201940f54646a4acdbbd37
Reviewed-on: http://gerrit.openafs.org/9393
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>