samples: net: sockets: sntp_client: build for native_posix

Extend the sample to be built with native_posix
prevent issues like #57133 in the future. Also extends the qemu
build to build a "raw" configurationw without POSIX_API or
NET_SOCKETS_POSIX_NAMES.

Signed-off-by: Hein Wessels <heinwessels93@gmail.com>