samples: net: socketpair: ensure integration platform is on allow list

Ensure that qemu_x86 (the integration platform) is on the allow list
for `sample.net.sockets.socketpair.s32k148_evb`.

```
INFO: Error found: sample.net.sockets.socketpair.s32k148_evb on
qemu_x86/atom (Not in testsuite platform allow list but is one of the
integration platforms)
```

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>