Fix: resolve race in networking layer assigning write operation to key

[GalRogozinski]

Description of change

Tries to solve the syncing problem from #1863 by synchronizing between registering of operation to keys, to ensure no race conditions...

Type of change

• Bug fix (a non-breaking change which fixes an issue)

How the change has been tested

It was ran w.o. data races and no noticeable sync slow down

Change checklist

• My code follows the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[DyrellC]

LGTM, and I synced a node using this code from 15k milestones back on mainnet, green lights all around. No stalls.