ofproto: Add "ofproto/trace" command to help debugging flow tables.

ofproto: Add "ofproto/trace" command to help debugging flow tables.

With an appropriate flow table, output from a command like this:

ovs-appctl ofproto/trace system@dp0 0 0 ffffffffffff000c29f49d5c080600010
80006040001000c29f49d5cac10008a000000000000ac1004df00000000000000000000000000000
0000000

resembles the following:

Packet: -8:00:00.000000 00:0c:29:f4:9d:5c > ff:ff:ff:ff:ff:ff, ethertype ARP (0x
0806), length 60: arp who-has 172.16.4.223 tell 172.16.0.138
Flow: tunnel0:in_port0000:tci(0) mac00:0c:29:f4:9d:5c->ff:ff:ff:ff:ff:ff type080
6 proto1 tos0 ip172.16.0.138->172.16.4.223 port0->0
Rule: cookie=0 in_port=65534
OpenFlow actions=resubmit:1,mod_vlan_vid:5,resubmit:2,mod_vlan_pcp:6,strip_vlan

        Resubmitted flow: unchanged
        Rule: cookie=0 in_port=1
        OpenFlow actions=resubmit:3,resubmit:4

                Resubmitted flow: unchanged
                No match

                Resubmitted flow: unchanged
                No match

        Resubmitted flow: tunnel0:in_port0000:tci(vlan5,pcp0) mac00:0c:29:f4:9d:
5c->ff:ff:ff:ff:ff:ff type0806 proto1 tos0 ip172.16.0.138->172.16.4.223 port0->0
        No match

Final flow: tunnel0:in_port0000:tci(0) mac00:0c:29:f4:9d:5c->ff:ff:ff:ff:ff:ff t
ype0806 proto1 tos0 ip172.16.0.138->172.16.4.223 port0->0
Datapath actions: set_tci(vid=5,pcp=0),set_tci(vid=5,pcp=6),strip_vlan