net + posix: avoid host includes when building for native_sim

A corner case involving C++, posix, networking, and native_sim
was causing problems.

Even though C and C++ builds should include zephyr/posix/.. in
the default search path with `CONFIG_POSIX_API=y`, for some
reason, the native compiler pulls in /usr/include first anyway.

The stat.h header pulled in <sys/types.h> (which is normally
fine) but due to the native build, it was pulling in
/usr/include/sys/types.h, from the host toolchain.

Explicitly include <zephyr/posix/posix_types.h> instead of
<sys/types.h> from stat.h, and continue using the workarounds
for native builds (explicitly including zephyr/posix/arpa/net.h
from net/sockets.h .

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
(cherry picked from commit 81f52050)