Add a patch for scapy to fix fd leak issue in AsyncSniffer (sonic-net…

…#20415)

Why I did it
This PR is to add a patch to fix potential fd leak issue in AsyncSniffer in scapy python library.
There are two fd leak scenarios.

When starting worker thread _run, if an interface is down, an OSError is thrown, and the sockets that have been created will be leaked as it never got a chance to be closed.
When stopping the worker thread, same error can happen when calling close. The sockets not closed will be leaked.

How I did it
Catch OSError when creating sockets, and catch any exception when closing socket to ensure all sockets are closed.

How to verify it
Verified by the testing code above. No fd leak happened.

src/scapy.patch/0004-Fix-fd-leak-in-worker-thread.patch

@@ -0,0 +1,47 @@
+diff --git a/scapy/sendrecv.py b/scapy/sendrecv.py
+index f97fc415..dbcc372f 100644
+--- a/scapy/sendrecv.py
++++ b/scapy/sendrecv.py
+@@ -1111,17 +1111,19 @@ class AsyncSniffer(object):
+             # The _RL2 function resolves the L2socket of an iface
+             _RL2 = lambda i: L2socket or resolve_iface(i).l2listen()  # type: Callable[[_GlobInterfaceType], Callable[..., SuperSocket]]  # noqa: E501
+             if isinstance(iface, list):
+-                sniff_sockets.update(
+-                    (_RL2(ifname)(type=ETH_P_ALL, iface=ifname, **karg),
+-                     ifname)
+-                    for ifname in iface
+-                )
++                for ifname in iface:
++                    try:
++                        sniff_sockets.update({_RL2(ifname)(type=ETH_P_ALL, iface=ifname, **karg): ifname})
++                    except OSError:
++                        # Ignore OSError when opening the socket
++                        # The error can happen when the port goes down during the creation of the socket
++                        pass
+             elif isinstance(iface, dict):
+-                sniff_sockets.update(
+-                    (_RL2(ifname)(type=ETH_P_ALL, iface=ifname, **karg),
+-                     iflabel)
+-                    for ifname, iflabel in six.iteritems(iface)
+-                )
++                for ifname, iflabel in six.iteritems(iface):
++                    try:
++                        sniff_sockets.update({_RL2(ifname)(type=ETH_P_ALL, iface=ifname, **karg): iflabel})
++                    except OSError:
++                        pass
+             else:
+                 iface = iface or conf.iface
+                 sniff_sockets[_RL2(iface)(type=ETH_P_ALL, iface=iface,
+@@ -1221,7 +1223,11 @@ class AsyncSniffer(object):
+         self.running = False
+         if opened_socket is None:
+             for s in sniff_sockets:
+-                s.close()
++                try:
++                    s.close()
++                except Exception:
++                    # Ignore exceptions to ensure all sockets are closed
++                    pass
+         elif close_pipe:
+             close_pipe.close()
+         self.results = session.toPacketList()

src/scapy.patch/series

@@ -1,3 +1,4 @@
 0001-Fix-version-string-generation-when-scapy-is-a-submod.patch
 0002-Check-if-the-network-interface-still-exists.patch
 0003-Do-not-resolve-the-interface-name-globally.patch
+0004-Fix-fd-leak-in-worker-thread.patch