[TR]: Use ctl paths to register net/token-ring/ table

The same thing for token-ring - use ctl paths and get
rid of external references on the tr_table.

Unfortunately, I couldn't split this patch into cleanup and
use-the-paths parts.

As a lame excuse I can say, that the cleanup is just moving
the tr_table from one file to another - closet to a single
variable, that this ctl table tunes. Since the source  file
becomes empty after the move, I remove it.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>