skge: fix transmitter flow control

It looks like the skge driver inherited another bug from the sk98lin code.
If I send from 1000mbit port to a machine on 100mbit port, the switch should
be doing hardware flow control, but no pause frames show up in the statistics.

This is the analog of the recent sky2 fixes. The device needs to listen
for multicast pause frames and then not discard them.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>