Enable BIP157 block filters index and serving by default

This change enables compact block filters (BIP157) functionality by default:
- Sets DEFAULT_BLOCKFILTERINDEX to "basic" instead of "0"
- Sets DEFAULT_PEERBLOCKFILTERS to true instead of false

This improves privacy for light clients and enables better pruned node support.

Author: PastaPastaPasta

src/net_processing.h

@@ -33,7 +33,7 @@ static const unsigned int DEFAULT_MAX_ORPHAN_TRANSACTIONS_SIZE = 10; // this all
 /** Default number of orphan+recently-replaced txn to keep around for block reconstruction */
 static const unsigned int DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN = 100;
 static const bool DEFAULT_PEERBLOOMFILTERS = true;
-static const bool DEFAULT_PEERBLOCKFILTERS = false;
+static const bool DEFAULT_PEERBLOCKFILTERS = true;
 /** Threshold for marking a node to be discouraged, e.g. disconnected and added to the discouragement filter. */
 static const int DISCOURAGEMENT_THRESHOLD{100};
 

src/validation.h

@@ -79,7 +79,7 @@ static const int64_t DEFAULT_MAX_TIP_AGE = 6 * 60 * 60; // ~144 blocks behind ->
 static const bool DEFAULT_CHECKPOINTS_ENABLED = true;
 static const bool DEFAULT_TXINDEX = true;
 static constexpr bool DEFAULT_COINSTATSINDEX{false};
-static const char* const DEFAULT_BLOCKFILTERINDEX = "0";
+static const char* const DEFAULT_BLOCKFILTERINDEX = "basic";
 /** Default for -persistmempool */
 static const bool DEFAULT_PERSIST_MEMPOOL = true;
 /** Default for -syncmempool */