sky2: allow multicast pause frames

The 802 standard allows pause frames to be either unicast or multicast.
Switches seem to send unicast frames, but on a direct link, other boards send
multicast pause.  Unless the filter bit is set, these pause frames get
dropped.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>