tests/kernel/smp: Honor TEST_EXTRA_STACKSIZE
tests/kernel/smp: Honor TEST_EXTRA_STACKSIZE

There was a test-created thread that wasn't including this.  It's a
huge stack and doesn't overflow (though I thought briefly that it
was), but it's a rule that we need to have that buffer and I'm trying
to fix these as I find them.

Signed-off-by: Andy Ross <c70f9a6bf6ee0cd69c8af4ce5e6b131945769315@intel.com>

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