Context

Tezos P2P protocol offers 2 ways for a node to inform its neighbors that its head changed:

Sending only this new head assuming the neighbor should know about its predecessor
Sending a "locator" a sparse description of the full chain history in order for the 2 nodes to agree on a common known ancestor and sync a full branch from it launching a "bootstrap pipeline".

This MR improve 2 situations:

When you receive a "locator" but actually you know all the blocks up to the predecessor of the head, it's useless to launch a bootstrap pipeline, applying the block is enough
When you switch head to a block of same level (but higher round), your neighbors should also know about the new head predecessor so it's enough to send the new head.

Manually testing the MR

Launch a node in verbose mode on a network with some history and check your logs

Document the interface of any function added or modified (see the coding guidelines)
Document any change to the user interface, including configuration parameters (see node configuration)
Provide automatic testing (see the testing guide).
For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
Select suitable reviewers using the Reviewers field below.
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