Change l2-fwd node to allow possible feature before UU-FLOOD

Change l2-fwd node to allow possible feature before UU-FLOOD

If l2-fwd node does not find an L2FIB entry for DMAC of packet,
use input feature bitmap to find next node instead of always
sending packet to l2-flood node to perform unknow unicast flood.
It provides possibilty of using other feature to forward unknow
unicast packet instead of flooding the BD.

Change-Id: I56b277050537678c92bd548d96d87cadc8d2e287
Signed-off-by: John Lo <loj@cisco.com>
(cherry picked from commit 9a719298c3160b0c28aa7d74747ef206751c8cae)