tests: net: context: Fix tests when using locking
tests: net: context: Fix tests when using locking

There was a false timeout error because we did not check the
return value correctly. This issue is seen now because code
flow in core IP stack is happening in different order than
before.

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

zephyrproject-rtos/zephyr,ldts/zephyr,explora26/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,explora26/zephyr,ldts/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,galak/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,galak/zephyr,finikorg/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,finikorg/zephyr,explora26/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,finikorg/zephyr,nashif/zephyr