SUNRPC: stop printk reading past end of string

Since p points at raw xdr data, there's no guarantee that it's NULL
terminated, so we should give a length.  And probably escape any special
characters too.

Reported-by: Zhi Li <yieli@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>