lib: os: mpsc_buf: Allow dropping of skip packets in no overwrite
lib: os: mpsc_buf: Allow dropping of skip packets in no overwrite

Previously, when no overwrite mode was used and there was no space
no packet was dropped. However, it should be allowed to drop skip
packet that may be added as padding at the end of the buffer.
Extended dropping scheme to drop skip packets in no overwrite mode.

Signed-off-by: Krzysztof Chruscinski <9b6dc988558c51b0405b49b55c8e66862969844b@nordicsemi.no>

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