Fix AsyncSniffer Attribute Error

[louis-6wind]

Fix scenario:

from scapy.all import AsyncSniffer
sniffer=AsyncSniffer(
... iface="br100",
... store=False,
... promisc=False,
... )
sniffer.start()
sniffer.stop()
Traceback (most recent call last):
File "", line 1, in
File "/usr/local/lib/python3.12/dist-packages/scapy/sendrecv.py", line 1404, in stop
if self.continue_sniff:
^^^^^^^^^^^^^^^^^^^
AttributeError: 'AsyncSniffer' object has no attribute 'continue_sniff'

Related to #4781 (comment)

Checklist:

• If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
• I executed the regression tests (using cd test && ./run_tests or tox)
• If the PR is still not finished, please create a Draft Pull Request

fixes #xxx

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.03%. Comparing base (b54fdb7) to head (3dc5a88).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4800      +/-   ##
==========================================
+ Coverage   80.08%   81.03%   +0.95%     
==========================================
  Files         365      365              
  Lines       89027    89027              
==========================================
+ Hits        71296    72143     +847     
+ Misses      17731    16884     -847     

Files with missing lines	Coverage Δ
scapy/sendrecv.py	86.53% <100.00%> (ø)

... and 26 files with indirect coverage changes

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