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

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.03%. Comparing base (5744d95) to head (19e5e86).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/sendrecv.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4800      +/-   ##
==========================================
- Coverage   81.03%   81.03%   -0.01%     
==========================================
  Files         365      365              
  Lines       89029    89033       +4     
==========================================
+ Hits        72141    72144       +3     
- Misses      16888    16889       +1     

Files with missing lines	Coverage Δ
scapy/sendrecv.py	86.47% <75.00%> (-0.07%)	⬇️

... and 4 files with indirect coverage changes

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[gpotter2]

Thanks for the PR !