Update: process monitor events all at once upon commit

[Ignatella]

Hi!

While using nftables, we discovered it would be more efficient to process monitor events (changes) all at once upon commit, triggered by the event that caused the change, such as NFT_MSG_NEWGEN.

This PR modifies the way events are handled by grouping all changes together and processing them in response to the event that initiated the change. Additionally, the event header, which includes important information such as the PID, is now propagated. This allows us to identify the process responsible for the change.