tests: bluetooth: mesh_shell: Disable BT_EXT_ADV for qemu_cortex_m3
tests: bluetooth: mesh_shell: Disable BT_EXT_ADV for qemu_cortex_m3

mesh_shell sample doesn't fit into flash with the extended advertising.

Signed-off-by: Pavel Vasilyev <09eaab7002a868ff10244a9e1218e073869f50ea@nordicsemi.no>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,galak/zephyr