Added logic to compute ICRC for RoCEv2 over IPv6

[leonidokner-enf]

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

Merging #4154 (48e07fe) into master (2a4c4ae) will decrease coverage by 0.01%.
Report is 2 commits behind head on master.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4154      +/-   ##
==========================================
- Coverage   81.77%   81.76%   -0.01%     
==========================================
  Files         330      330              
  Lines       76290    76315      +25     
==========================================
+ Hits        62383    62398      +15     
- Misses      13907    13917      +10     

Files	Coverage Δ
scapy/contrib/roce.py	95.18% <100.00%> (+1.15%)	⬆️

... and 6 files with indirect coverage changes