Changeset 243ddb52 in rtems for bsps

leon,greth: enable MAC filtering (promiscous mode, multicast)

It enabled promiscous mode or sets the multicast filter according
to the configuration and parameters to ioctl(SIOCSIFFLAGS),
ioctl(SIOCADDMULTI) and ioctl(SIOCDELMULTI).
On SIOCADDMULTI/SIOCDELMULTI requests the greth ioctl calls the
Ethernet helper functions ether_addmulti()/ether_delmulti() which
tells the greth driver when its required to update the MAC multicast
filtering.

The interface notifies support for multicast by setting IFF_MULTICAST.

The GRETH has two registers which contains a bit-mask of allowed MAC
addresses. The incomming MAC address is CRC:ed and the CRC is used as
an index into the bit-mask to determine to allow or drop the frame.