Option to forward BPDU (Ethernet control class) frames

Option to forward BPDU (Ethernet control class) frames

Currently, a NORMAL action bridge drops reserved-multicast-mac addresses;
01-80-c2-00-00-[f0:ff]. A node that does not implement STP should have an
option to forward such frames.

This commit proposes to have a configuration option to allow forwarding of
BPDU class frames.  To ensure backward compatibility, this option is
disabled by default.

This config can be set using bridge's other-config column, for e.g
ovs-vsctl set bridge br0 other-config:forward-bpdu=true

Changing this option can revalidate all flows in a software-OVS
implementation (ofproto-dpif)

--------
unit tests:

------------
make config changes, test runtime behavior

-- test runtime behavior --
continuously send packets to br0 with dest-mac=01:80:c2:00:00:00

ovs-dpctl dump-flows br0
ovs-vsctl set bridge br0 other-config:forward-bpdu=true
ovs-dpctl dump-flows br0
ovs-vsctl set bridge br0 other-config:forward-bpdu=false
ovs-dpctl dump-flows br0
ovs-vsctl set bridge br0 other-config:forward-bpdu=true
ovs-dpctl dump-flows br0
ovs-vsctl remove bridge br0 other-config forward-bpdu=true
ovs-dpctl dump-flows br0

--result--
 ovs-dpctl dump-flows br0
 in_port(1),eth(src=00:0c:29:d1:39:42,dst=01:80:c2:00:00:00), packets:29550, bytes:1773000, used:0.004s, actions:drop
 ovs-vsctl set bridge br0 other-config:forward-bpdu=true

 ovs-dpctl dump-flows br0
in_port(1),eth(src=00:0c:29:d1:39:42,dst=01:80:c2:00:00:00), packets:8209, bytes:492540, used:0.000s, actions:2,0

 ovs-vsctl set bridge br0 other-config:forward-bpdu=false
 ovs-dpctl dump-flows br0
in_port(1),eth(src=00:0c:29:d1:39:42,dst=01:80:c2:00:00:00), packets:19, bytes:1140, used:0.000s, actions:drop

 ovs-vsctl set bridge br0 other-config:forward-bpdu=true
 ovs-dpctl dump-flows br0
in_port(1),eth(src=00:0c:29:d1:39:42,dst=01:80:c2:00:00:00), packets:29, bytes:1740, used:0.000s, actions:2,0

 ovs-vsctl remove bridge br0 other-config forward-bpdu=true
 ovs-dpctl dump-flows br0
in_port(1),eth(src=00:0c:29:d1:39:42,dst=01:80:c2:00:00:00), packets:0, bytes:0, used:never, actions:drop

Bug #6624
Reported-by: Niklas Andersson <nandersson@nicira.com>