x/net/ipv4: TestPacketConnReadWriteUnicastUDP failures with `i/o timeout`

[gopherbot]

#!watchflakes
post <- pkg == "golang.org/x/net/ipv4" && test == "TestPacketConnReadWriteUnicastUDP" && `i/o timeout`

Issue created automatically to collect these failures.

Example (log):

--- FAIL: TestPacketConnReadWriteUnicastUDP (0.10s)
    unicast_test.go:79: read udp 127.0.0.1:65493: raw-read udp4 127.0.0.1:65493: i/o timeout

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
post <- pkg == "golang.org/x/net/ipv4" && test == "TestPacketConnReadWriteUnicastUDP"

2023-01-05 16:42 netbsd-amd64-9_3 net@f8411da7 go@145dd384 x/net/ipv4.TestPacketConnReadWriteUnicastUDP (log)

--- FAIL: TestPacketConnReadWriteUnicastUDP (0.10s)
    unicast_test.go:79: read udp 127.0.0.1:65493: raw-read udp4 127.0.0.1:65493: i/o timeout

— watchflakes

[bcmills]

See previously #53402.