[dualtor][sniffer] Explicitly set listen ports (#18299) (#18362)

What is the motivation for this PR?
On scapy with version v2.40 and under, the sniffer will capture packets on every interface if no interface is given.
On scapy with version v.2.50 and higher, the sniffer will capture packets on conf.iface if no interface is given; on the ptf, conf.iface is mgmt, so dual_tor_sniffer is not able to capture any meaningful dataplane packets.

secdev/scapy#1420

Signed-off-by: Longxiang Lyu lolv@microsoft.com

How did you do it?
Let dual_tor_sniffer explicitly sniff on dataplane ports (any ptf ports starting with eth)

How did you verify/test it?
Run dualtor I/O testcase.

Signed-off-by: Longxiang Lyu <lolv@microsoft.com>
Co-authored-by: Longxiang Lyu <35479537+lolyu@users.noreply.github.com>

Author: mssonicbld

tests/scripts/dual_tor_sniffer.py

@@ -1,11 +1,13 @@
 import argparse
 import logging
+import socket
 
 import scapy.all as scapyall
 
 
 class Sniffer(object):
     def __init__(self, filter=None, timeout=60):
+        self.ifaces = [iface for _, iface in socket.if_nameindex() if iface.startswith("eth")]
         self.filter = filter
         self.timeout = timeout
         self.packets = []
@@ -15,6 +17,7 @@ def sniff(self):
         logging.debug("scapy sniffer started: filter={}, timeout={}".format(
             self.filter, self.timeout))
         scapyall.sniff(
+            iface=self.ifaces,
             filter=self.filter,
             prn=self.process_pkt,
             timeout=self.timeout)