Fix the formatting of antctl trace-packet output

[jianjuns]

Transform the "/ovstracing API" response to []byte, and change antctl to
output the raw bytes directly for a []byte type response.

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[lzhecheng]

Will you change /ovsflows as well since its response type ovsflows.Response has similar struct with ovstracing.Response? I am wondering the purpose of this PR.

[jianjuns]

@lzhecheng : I should mention the reason for this change is because the trace-packet formatting is broken now:

result: "Flow: ip,in_port=2,vlan_tci=0x0000,dl_src=ce:4f:c2:58:8a:be,dl_dst=00:00:00:00:00:00,nw_src=172.100.0.1,nw_dst=0.0.0.0,nw_proto=0,nw_tos=0,nw_ecn=0,nw_ttl=64\n\nbridge("br-int")\n----------------\n 0. in_port=2, priority 200, cookie 0x14000000000000\n load:0x1->NXM_NX_REG0[0..15]\n goto_table:10\n10. ip,in_port=2, priority 200, cookie 0x14000000000000\n goto_table:29\n29. priority 0, cookie 0x14000000000000\n goto_table:30\n30. ip, priority 200, cookie 0x14000000000000\n ct(table=31,zone=65520,nat)\n nat\n -> A clone of the packet is forked to recirculate. The forked pipeline will be resumed at table 31.\n -> Sets the packet to an untracked state, and clears all the conntrack fields.\n\nFinal flow: ip,reg0=0x1,in_port=2,vlan_tci=0x0000,dl_src=ce:4f:c2:58:8a:be,dl_dst=00:00:00:00:00:00,nw_src=172.100.0.1,nw_dst=0.0.0.0,nw_proto=0,nw_tos=0,nw_ecn=0,nw_ttl=64\nMegaflow: recirc_id=0,eth,ip,in_port=2,nw_dst=0.0.0.0/1,nw_frag=no\nDatapath actions: ct(zone=65520,nat),recirc(0x1)\n\n===============================================================================\nrecirc(0x1) - resume conntrack with default ct_state=trk|new (use --ct-next to customize)\nReplacing src/dst IP/ports to simulate NAT:\n Initial flow: \n

/ovsflows is different - it returns an array of flows, but not a single string.

[lzhecheng]

LGTM

[tnqn]

LGTM

[jianjuns]

/test-all