fix(libkernel): accept guest socket addresses whatever their sa_len

[kjhq]

What

bind, connect, sendto and the other socket calls rejected an address whose sa_len byte (byte 0) was not exactly 16 for IPv4 or 28 for IPv6. The FreeBSD kernel does not read sa_len on input: getsockaddr overwrites it with the length argument. A title that leaves sa_len 0 got EAFNOSUPPORT (47), which the console does not return for it.

Now the family byte and the length argument alone decide the address kind; addresses returned to the guest still carry the correct sa_len.

• guest_udp: binding 127.0.0.1 with sa_len 0 succeeds and getsockname reports sa_len 16.

Title

PPSA17221 (Minecraft) needs #716 to load the modules in its app root, so every run below is current main + #716 + the PRs of this set (#1088, #1090–#1096), plus local changes outside it: dialog, NpAuth and TextToSpeech2 stubs that open PRs cover (#560, #925, #301) and a GPU end-of-pipe change that is not submitted. With all of them the title loads a world. The line below is from a run with only this PR left out, Windows 11, WinLibs GCC, normal user session.

Without it the title crashes about 12 s after start:

FATAL: unhandled exception 0xc0000005 on thread 5288 'MINECRAFT MAIN THREAD'
  rip 0x00007ff71ba02c2b app.exe+0x51d2c2b
  read of 0x0000000000000000

With it, the title reaches a loaded world.

Tested

Debian 13 (WSL2), GCC 14.2.0, Release: guest_udp and guest_tcp pass. The new check fails on main without the fix.

Windows 11, WinLibs GCC: PPSA17221 with this PR and the rest of the set loads a world (runs described above). Not tested with Windows ctest.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed in TechnicalDebt
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• AI-assisted: yes

🤖 Generated with Claude Code

[TheAggie]

Another title this fixes: the DOOM homebrew PPSA99666 v1.1.1 (lowbit/ps5-doom) zeroes its sockaddr_in and sets only the family and port, so its upload server's bind failed on every port:

[debug:0] upload: port 9666 refused (error 47)
...
[debug:0] upload: port 9673 refused (error 47)

With the same change (I had made it independently before finding this PR), the server binds and, together with poll and MSG_NOSIGNAL support, served its page and received a 28.8 MB WAD intact. Windows 11, MinGW GCC 15.2.0 (WinLibs r7), RTX 5070 Ti.

[adriadam10]

Checked: build + full ctest on current main + this PR (416/416), guest_udp fails with the Udp.cpp change reverted, Linux and Windows CI green. Matches FreeBSD getsockaddr, which ignores the input sa_len; returned addresses still carry the right one. Merging.