WIP - Fix IP options injection and parsing.

[rafaelroquetto]

This PR addresses a few issues with the IP options mechanism namely:

1. deal with IP headers already containing IP options, ensuring they are not corrupt
2. fix a broken assumption that tc ingress == request ingress path (and likewise, tc egress == request egress path). This is not always true. In k8s for instance, we end up attaching to the host veth of a given service pod, which will see traffic leaving the POD as ingress (pod eth0 (egress) ----> (ingress) host veth).

Also add a unit test.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.26%. Comparing base (5438915) to head (6ca1022).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #933   +/-   ##
=======================================
  Coverage   55.26%   55.26%           
=======================================
  Files         253      253           
  Lines       21769    21769           
=======================================
  Hits        12031    12031           
  Misses       8911     8911           
  Partials      827      827           

Flag	Coverage Δ
integration-test	23.23% <ø> (-0.02%)	⬇️
integration-test-arm	?
integration-test-vm-${ARCH}-${KERNEL_VERSION}	0.00% <ø> (ø)
k8s-integration-test	2.73% <ø> (ø)
oats-test	0.00% <ø> (ø)
unittests	46.40% <ø> (ø)

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