samples: net: echo_server: add runtime test for NSOS net init

Expect that networking is properly setup, by expecting
NET_EVENT_L4_CONNECTED event and listening for TCP/UDP incoming traffic on
both IPv4 and IPv6.

Signed-off-by: Marcin Niestroj <[email protected]>
(cherry picked from commit 82b6140)

Author: mniestroj

samples/net/sockets/echo_server/sample.yaml

@@ -139,11 +139,21 @@ tests:
     integration_platforms:
       - qemu_x86
   sample.net.sockets.echo_server.nsos:
+    harness: console
     platform_allow:
       - native_sim
       - native_sim/native/64
     extra_args:
       - EXTRA_CONF_FILE="overlay-nsos.conf"
+    harness_config:
+      type: multi_line
+      ordered: false
+      regex:
+        - "Network connected"
+        - "Waiting for TCP.*IPv4"
+        - "Waiting for TCP.*IPv6"
+        - "Waiting for UDP.*IPv4"
+        - "Waiting for UDP.*IPv6"
   sample.net.sockets.echo_server.802154.subg:
     extra_args: EXTRA_CONF_FILE="overlay-802154-subg.conf"
     platform_allow: beagleconnect_freedom