tg3: Give MSI-X vec 1 rx backlog space

RSS ring 1 is responsible for submitting new rx buffers to the
hardware on behalf of all the other RSS rx return rings.  Up until now
this ring submitted its new rx buffers to the producer ring directly.
The following patch will require that this ring have a place to put
backlogged rx packets.  As a consequence, it can no longer submit new
buffers to the producer ring.

This patch adds code to allocate an extra shadow producer ring for this
RSS ring and adds RSS ring 1 to the list of rings needing buffer
transfers.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Reviewed-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>