drivres/net: Change constant name

In this series of tests the constants have the form XRXMAC_STATUS, except
in this one case.  The values of XRXMAC_STAT_MSK_RXOCTET_CNT_EXP and
XRXMAC_STATUS_RXOCTET_CNT_EXP are furthermore the same.

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>