Bugfix: rx descriptor release function fails to visit
the last entry while walking receive descriptor ring.
Signed-off-by: Linas Vepstas <linas@austin.ibm.com> Cc: James K Lewis <jklewis@us.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Jeff Garzik <jeff@garzik.org>