samples: net: dumb_http_server_mt: Fix the OK/FAIL status check
samples: net: dumb_http_server_mt: Fix the OK/FAIL status check

The test script http-get-file-test.sh will send a POST to inform
whether the test was ok or not. This is needed so that we can
test the TLS functionality properly, earlier use of netcat would
not do TLS handshakes.

Signed-off-by: Jukka Rissanen <f9f077d1da4c7aa947f9864fa5a28c3588f6a45d@linux.intel.com>

Vudentz/zephyr,finikorg/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr