doc: Consolidate NetRestrict format docmentation

doc: Consolidate NetRestrict format docmentation

We were specifying exactly the same format in two different places;
consolidate them into one place. In addition, explicitly say there are
is no way to specify a range of addresses, in case some people are
confused by the previous versions of this man page that erroneously
said you could use 255 as a wildcard.

Change-Id: I18d96ee9e6c43dfb62719323fa7eb8d9f254e273
Reviewed-on: http://gerrit.openafs.org/7565
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>