CPU reads across NTB are slow(er) and can hang the local system if an
ECC error is encountered on the remote.  To work around the need for a
read, have the remote side write its current position in the rx buffer
to the local system's buffer and use that to see if there is room when
transmitting.
Signed-off-by: NJon Mason <jon.mason@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>