net: eth: native_posix: Add missing headers

unistd.h was missing (used by read, close..)

printk header was also missing, but replace it's use
with posix_print_trace: It is faster and does not require
any Zephyr functionality to work.
fflush is not needed in this case.

Signed-off-by: Alberto Escolar Piedras <alpi@oticon.com>
1 file changed