Fix documentation to reflect reality
Use strcmp() rather than strncmp()

This results in some false positives. If the authfile contains:

192.168.0.12

and the client is

192.168.0.1

then access will be granted, because the strcmp was limiting to
"192.168.0.1" for no particularly good reason.

We should also canonicalize our names and work on that, rather than
doing a simple strcmp(), but that's for later.