net: macb: Handle the RXUBR interrupt on all devices

The same hardware issue the at91 must work around applies to at least the
Zynq ethernet, and possibly more devices.  The driver also needs to handle
the RXUBR interrupt since it turns it on with MACB_RX_INT_FLAGS anyway.

Signed-off-by: Nathan Sullivan <nathan.sullivan@ni.com>
Signed-off-by: David S. Miller <davem@davemloft.net>