tg3: Don't check undefined error bits in RXBD

[ Upstream commit d7b95315cc7f441418845a165ee56df723941487 ]

Redefine the RXD_ERR_MASK to include only relevant error bits. This fixes
a customer reported issue of randomly dropping packets on the 5719.

Change-Id: I7ae846a577b37a736ec2479d7a57bd601b34c5e0
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>