refactor(peer_loop): Limit block-batch size to 250

Ensure that messages with more than 250 blocks are never sent.

In e491b2e, the default reorganization
tolerance was increased from 100 to 1.000 blocks, and the max number of
blocks in these messages are affected by that value. So this commit
intends to prevent too big messages from being sent, as I though 1.000
blocks (~600MB) were too big messages.

src/peer_loop.rs

@@ -46,7 +46,7 @@ use crate::models::state::mempool::MEMPOOL_IGNORE_TRANSACTIONS_THIS_MANY_SECS_AH
 use crate::models::state::mempool::MEMPOOL_TX_THRESHOLD_AGE_IN_SECS;
 use crate::models::state::GlobalStateLock;
 
-const STANDARD_BLOCK_BATCH_SIZE: usize = 50;
+const STANDARD_BLOCK_BATCH_SIZE: usize = 250;
 const MAX_PEER_LIST_LENGTH: usize = 10;
 const MINIMUM_BLOCK_BATCH_SIZE: usize = 2;
 
@@ -643,14 +643,16 @@ impl PeerLoopHandler {
                 );
 
                 // Get the relevant blocks, at most batch-size many, descending from the
-                // peer's (alleged) most canonical block.
+                // peer's (alleged) most canonical block. Don't exceed `max_response_len`
+                // or `STANDARD_BLOCK_BATCH_SIZE` number of blocks in response.
                 let len_of_response = cmp::min(
                     max_response_len,
                     self.global_state_lock
                         .cli()
                         .max_number_of_blocks_before_syncing,
                 );
                 let len_of_response = cmp::max(len_of_response, MINIMUM_BLOCK_BATCH_SIZE);
+                let len_of_response = cmp::min(len_of_response, STANDARD_BLOCK_BATCH_SIZE);
 
                 let mut digests_of_returned_blocks = Vec::with_capacity(len_of_response);
                 let response_start_height: u64 = peers_preferred_canonical_block.into();