x/net/internal/quic: `TestUDPECN` consistently failing with `EINVAL` on big-endian Linux ports since CL 565255

[bcmills]

Go version

b27d02c

Output of go env in your module/workspace:

N/A

What did you do?

Check https://build.golang.org/?repo=golang.org%2fx%2fnet.

What did you see happen?

https://build.golang.org/log/c4023ea6a7dc8a2d6997c34c4bf6a0e8caf0b203:

--- FAIL: TestUDPECN (0.00s)
    --- FAIL: TestUDPECN/udp4/udp/unspec (0.00s)
        udp_test.go:88: Write: write udp4 127.0.0.1:41802->127.0.0.1:49627: sendmsg: invalid argument
    --- FAIL: TestUDPECN/udp4/udp4/unspec (0.00s)
        udp_test.go:88: Write: write udp4 127.0.0.1:53832->127.0.0.1:58021: sendmsg: invalid argument
    --- FAIL: TestUDPECN/udp4/udp4/spec (0.00s)
        udp_test.go:88: Write: write udp4 127.0.0.1:35689->127.0.0.1:58919: sendmsg: invalid argument
FAIL
FAIL	golang.org/x/net/internal/quic	0.982s

What did you expect to see?

All tests passing.

(attn @neild @jba)

[bcmills]

This failure mode affects ppc64, mips, mips64, and s390x — all big-endian architectures.

[gopherbot]

Change https://go.dev/cl/566098 mentions this issue: quic: temporarily disable networking tests failing on various platforms

[gopherbot]

Change https://go.dev/cl/566296 mentions this issue: quic: fix UDP on big-endian Linux, tests on various architectures