defconfig: Increase the size of RTT console "UP" buffer
defconfig: Increase the size of RTT console "UP" buffer

This change allows usage of larger RTT "UP" buffers from target to host.
It is necessary to allow correct execution of ping command:

net ping 192.168.0.1

Signed-off-by: Lukasz Majewski <7acbb0643e3da1a0f6f894ebd720fb3807e67dff@denx.de>

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