samples: net: echo_poll_test sample app

Simple app that just creates IPv4 and IPv6 TCP sockets, starts
to listen them. If there is a incoming connection, it will launch
a thread and pass the accepted socket to it. The thread will
echo all data back that is sent to it.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

Author: jukkar

samples/net/sockets/echo_poll_test/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.13.1)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(socket_poll_echo)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})
+
+include(${ZEPHYR_BASE}/samples/net/common/common.cmake)

samples/net/sockets/echo_poll_test/Makefile.posix

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+# This makefile builds sample for POSIX system, like Linux
+
+socket_poll_echo: src/main.c
+	$(CC) $^ -o $@ -lpthread
+
+clean:
+	rm -f socket_poll_echo

samples/net/sockets/echo_poll_test/README.rst

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+.. _sockets-poll-echo-sample:

samples/net/sockets/echo_poll_test/prj.conf

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+# General config
+CONFIG_NEWLIB_LIBC=y
+CONFIG_MAIN_STACK_SIZE=2048
+CONFIG_THREAD_NAME=y
+CONFIG_KERNEL_SHELL=y
+
+# Networking config
+CONFIG_NETWORKING=y
+CONFIG_NET_IPV4=y
+CONFIG_NET_IPV6=y
+CONFIG_NET_TCP=y
+CONFIG_NET_SOCKETS=y
+CONFIG_NET_SOCKETS_POSIX_NAMES=y
+CONFIG_NET_SOCKETS_POLL_MAX=15
+
+# Network driver config
+CONFIG_TEST_RANDOM_GENERATOR=y
+
+# Network address config
+CONFIG_NET_CONFIG_SETTINGS=y
+CONFIG_NET_CONFIG_NEED_IPV4=y
+CONFIG_NET_CONFIG_NEED_IPV6=y
+CONFIG_NET_CONFIG_MY_IPV4_ADDR="192.0.2.1"
+CONFIG_NET_CONFIG_PEER_IPV4_ADDR="192.0.2.2"
+CONFIG_NET_CONFIG_MY_IPV6_ADDR="2001:db8::1"
+CONFIG_NET_CONFIG_PEER_IPV6_ADDR="2001:db8::2"
+
+CONFIG_NET_SHELL=y