struct timeval is per POSIX defined in sys/time.h, but that also
allowed to pull sys/select.h (and indeed, it does with native_posix),
which then starts to conflict with out select implementation (if
NET_SOCKETS_POSIX_NAMES is defined, and many samples/tests have it).
So, for now follow the existing route of duplicating all definitions
needed by our code in namespaced manner. Things like struct timeval
usage will need to be revisited later, when we'll want socket
subsystem to work with POSIX subsystem, but that's a separate deep
matter.
Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>