Tests: Bluetooth: Mesh: Mesh shell prj stack size

Increases the main stack size of the mesh shell test application.
This resolves issue where application is not able to pass initialization
step.

Signed-off-by: Anders Storrø <anders.storro@nordicsemi.no>

Author: Andrewpini

tests/bluetooth/mesh_shell/prj.conf

@@ -1,7 +1,7 @@
 CONFIG_TEST=y
 CONFIG_TEST_LOGGING_DEFAULTS=n
 #CONFIG_INIT_STACKS=y
-CONFIG_MAIN_STACK_SIZE=504
+CONFIG_MAIN_STACK_SIZE=1024
 CONFIG_ISR_STACK_SIZE=1024
 CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048
 CONFIG_SHELL_STACK_SIZE=1728