Update mcumgr library to fix wrong callback state

[nordicjm]

Describe the bug
mcumgr's library has callbacks which report the status of a firmware update with 3 states - start, ongoing and complete. However, complete is not used.

This is fixed in this PR to the upstream mynewt-mcumgr project code: apache/mynewt-mcumgr#137

Therefore this is a request to pull the change into zephyr's version of mcumgr so that it will be included for Zephyr 2.7

[de-nordic]

@carlescufi @lairdjm I will include this into snapshot update.

[de-nordic]

Included here: zephyrproject-rtos/mcumgr#43

[de-nordic]

@cfriedt This is low priority bug, so it will not go into the 2.7. Should we re-target it? Also the bug is in the mcumgr rather than in Zephyr, in common code, so is it needed to keep this as a bug here? It has already been fixed in mcumgr but we are not able to change west.yml to include the fix at this point.

[cfriedt]

@de-nordic - we should be able to pull into main. What is preventing the west.yml update?

[de-nordic]

@cfriedt The mcumgr updates come in snapshot updates. To bring this fix in we would need to bring in features/enhancements that ere not "blockers".
Alternative is to create mcumgr-zephyr-2.7-lts branch and start bringing the fixes there, and use this branch in west.yml for lts.
Do we want to start the mcumgr-zephyr-2.7-lts branch already? It may happen anyway.

[cfriedt]

@cfriedt The mcumgr updates come in snapshot updates. To bring this fix in we would need to bring in features/enhancements that ere not "blockers".

@de-nordic - should be ok for main

[nordicjm]

Is it possible to get this included in a 2.7 backport, just the bug fix not the addition of features? We currently manually have this patched in a modified 2.6 branch and the idea was we would scrap it when moving to 2.7 because the fix would be included, but if the idea is this won't be fixed in 2.7 then that really doesn't sit well for our development