Fix bugs if stopping sendpfast via Ctrl+C (#4690)

[badcodebuilder]

• Fix bugs if stopping sendpfast via Ctrl+C

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

fix absence of termination of subprocess in sendpfast function

fixes #4690

PS: There is no unit test case for sendpfast function, so skip the CI test. But I tested it localy and it worked.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 78.59%. Comparing base (a4f958b) to head (15f9bc2).

Files with missing lines	Patch %	Lines
scapy/sendrecv.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4691      +/-   ##
==========================================
- Coverage   82.13%   78.59%   -3.55%     
==========================================
  Files         361      336      -25     
  Lines       86830    81630    -5200     
==========================================
- Hits        71319    64157    -7162     
- Misses      15511    17473    +1962     

Files with missing lines	Coverage Δ
scapy/sendrecv.py	84.20% <0.00%> (-2.44%)	⬇️

... and 287 files with indirect coverage changes

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