Support P4.org In-band Network Telemetry (INT)

[jingfeihu]

1.support INT MX/MD mode. 2.support INT over IPv4/IPv6+TCP/UDP/VXLAN/GRE/GENEVE. 3.add 28 testcases for INT.

[codecov[bot]]

Codecov Report

Merging #4230 (5b44983) into master (d71014a) will decrease coverage by 34.22%. Report is 5 commits behind head on master. The diff coverage is 62.79%.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4230       +/-   ##
===========================================
- Coverage   81.77%   47.55%   -34.22%     
===========================================
  Files         331      325        -6     
  Lines       76721    71527     -5194     
===========================================
- Hits        62736    34016    -28720     
- Misses      13985    37511    +23526     

Files	Coverage Δ
scapy/layers/inet.py	22.40% <20.00%> (-48.21%)	:arrow_down:
scapy/contrib/int.py	82.35% <82.35%> (ø)
scapy/contrib/geneve.py	51.66% <40.00%> (-45.56%)	:arrow_down:

... and 255 files with indirect coverage changes

[polybassa]

Thanks for your PR. Your code looks good so far, besides my to comments.