ot: ping ten times will crash

[turon]

Description
I observed that an openthread device initiating a ping of 10x 100 bytes will crash:

ot cmd ping ff02::1 100 10

Build
Steps to reproduce the behavior:

1. cd samples/net/echo_client
2. mkdir -p build/nrf52
3. cd build/nrf52
4. cmake -GNinja -DCONF_FILE="prj.conf overlay-ot.conf" -DBOARD=nrf52840_pca10056 ../..
5. ninja
6. ninja flash
7. sudo minicom -D /dev/ttyACM0 -b 115200
8. ot cmd panid 0xabcd
9. ot cmd ifconfig up
10. ot cmd thread start
11. Setup a second node, flash, and run steps 8-10
12. ot cmd state --> confirm Leader on one node and Child or Router on the other
13. ot cmd ping ff02::1
14. Observe response
15. ot cmd ping ff02::1 100 10
16. Observe crash

Expected behavior
Expect to see 10 ping responses and shell app to continue to run.

[rlubos]

@turon I've identified the issue, apparently it's an OpenThread bug - it does not handle ping timer correctly for cli_console backend. I've posted a fix to the OpenThread:
openthread/openthread#3486

Once accepted and merged, we can update the OpenThread in Zephyr.

[jakub-uC]

@turon It seems to be fixed on shell side with PR #12747.