Minor compilation fixes

[GabrielGanne]

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• The code passes sudo make test

Changes:

This PR should only contain changes that have no functional impact, and only either fix compilation with some specific configuration option, or with some additional warnings enabled.
Those warnings were found while working on compiling with meson and trying to add warning_level=3.

Since they are all rather small, I'm submitting them in a single PR, but please feel free to pick or reject any number of them or request a separate PR if you prefer.

[fklassen]

I targeted the latest branch and now I have conflicts. Please resolve.

[GabrielGanne]

I rebased over branch 4.6.1-beta1 and removed one commit about ubsan that you already fixed.

For ref, the commit was GabrielGanne@503ccf5
Your fix for the same issue is 314e489
It does indeed fix the ubsan issue and is smaller, but causes some address-of-packed-member warnings to appear.
Eg.

../src/tcpedit/edit_packet.c:246:24: warning: taking address of packed member of ‘struct tcpr_icmpv4_hdr’ may result in an unaligned pointer value [-Waddress-of-packed-member]
  246 |         csum_replace16(&icmp->icmp_sum, old, new);

I' not sure anyone really cares about these warnings anymore since most HW support this now, but it's still worth noting.

From what I can tell, the other commits are still relevant (no other commit in the beta branch tries to address the same issue)