FlowVisor should drop STP BDPUs silently (and quickly)

[nbastin]

FlowVisor spends a lot of time logging things like this:

Nov 15 13:54:13 thermopylae -1>Nov 15 13:54:13 flowvisor: WARN none : No match for: OFMatch[in_port=72,dl_dst=01:00:0c:cc:cc:cd,dl_src=30:37:a6:d1:0d:17,dl_type=0x32,dl_vlan=65535,dl_vpcp=0,nw_dst=0.0.0.0,nw_src=0.0.0.0,nw_proto=0,nw_tos=0,tp_dst=0,tp_src=0]

In this case the packet is an STP BDPU, which should almost certainly get dropped at the edge of your openflow domain (although possibly making this a preference is in order).

There is a larger issue of FV incorrectly handling all packets with dl_type < 1500, for which I will file another issue.. :-)