Fix layers.inet6.neighsol timeout not actually being used

[mattdibi]

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

While working on a strictly timed test for IPv6 firewall we noticed that the neighsol function was not respecting the given timeout. Looking at the code it was apparent that the timeout variable was not actually used in the code. This PR fixes that.

For unit tests I might require some guidance...

[codecov]

Codecov Report

Merging #4310 (99a0af5) into master (42b98a2) will decrease coverage by 0.88%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4310      +/-   ##
==========================================
- Coverage   81.37%   80.49%   -0.88%     
==========================================
  Files         350      350              
  Lines       82282    82282              
==========================================
- Hits        66954    66231     -723     
- Misses      15328    16051     +723     

Files	Coverage Δ
scapy/layers/inet6.py	88.67% <100.00%> (ø)

... and 29 files with indirect coverage changes

[guedou]

Good catch! Thanks for this PR.