shares the lock on gossip when processing prune messages (#13339)

Processing prune messages acquires an exclusive lock on gossip:
https://github.com/solana-labs/solana/blob/55b0428ff/core/src/cluster_info.rs#L1824-L1825
This can be reduced to a shared lock if active-sets are changed to use
atomic bloom filters:
https://github.com/solana-labs/solana/blob/55b0428ff/core/src/crds_gossip_push.rs#L50

runtime/benches/bloom.rs

@@ -135,7 +135,6 @@ fn bench_add_hash_atomic(bencher: &mut Bencher) {
         for hash_value in &hash_values {
             bloom.add(hash_value);
         }
-        let bloom: Bloom<_> = bloom.into();
         let index = rng.gen_range(0, hash_values.len());
         if !bloom.contains(&hash_values[index]) {
             fail += 1;