Unix CM: We're disconnected if RW disconnected too

Unix CM: We're disconnected if RW disconnected too

At the moment, the Unix CM doesn't support entering a purely RO
disconnected mode (the historical AFS_IS_DISCONNECTED mode). If we
go disconnected, or reconnect we always toggle RW discon at the same
time as we toggle RO. Arguably, the RO disconnected mode should just
be removed, as it is now superceded.

For the moment, make it clear to the compiler that RW disconnected
implies RO disconnected, so that static analysis can make more sensible
decisions about code paths.

Change-Id: I7e2d04d2cf67740c6b6285950874c6a4eaeb0537
Reviewed-on: http://gerrit.openafs.org/7097
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>