tg3: Assign rx ret producer indexes by vector

When RSS is enabled, the status block format changes slightly.  The
"rx_jumbo_consumer", "reserved", and "rx_mini_consumer" members get
mapped to the other three rx return ring producer indexes.  This patch
introduces a new per-interrupt member which identifies which location
in the status block a particular vector should look for return ring
updates.

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