reap max bytes from the mempool & check transaction size

See ADR 020: Limiting txs size inside a block docs/architecture/adr-020-block-size.md

Refs #2035

rpc/client/rpc_test.go

@@ -242,7 +242,7 @@ func TestBroadcastTxSync(t *testing.T) {
 
 		require.Equal(initMempoolSize+1, mempool.Size())
 
-		txs := mempool.Reap(1)
+		txs := mempool.ReapMaxTxs(len(tx))
 		require.EqualValues(tx, txs[0])
 		mempool.Flush()
 	}