feat(messaging): restore target group size

- As to avoid node level issues that were best solved with AE, the delivery target size stipulated in reliable messaging was previously overridden. Now that AE is to be implemented also at node level, we can restore this value.

src/delivery_group.rs

@@ -13,7 +13,7 @@ use crate::{
     network::Network,
     peer::Peer,
     section::Section,
-    ELDER_SIZE,
+    supermajority, ELDER_SIZE,
 };
 use itertools::Itertools;
 use sn_messaging::DstLocation;
@@ -111,17 +111,19 @@ fn candidates(
         .sorted_by(|lhs, rhs| lhs.prefix.cmp_distance(&rhs.prefix, target_name))
         .map(|info| (&info.prefix, info.elders.len(), info.elders.values()));
 
-    let mut dg_size = ELDER_SIZE;
+    // gives at least 1 honest target among recipients.
+    let min_group_size = 1 + ELDER_SIZE - supermajority(ELDER_SIZE);
+    let mut dg_size = min_group_size;
     let mut nodes_to_send = Vec::new();
     for (idx, (prefix, len, connected)) in sections.enumerate() {
         nodes_to_send.extend(connected.cloned());
         // If we don't have enough contacts send to as many as possible
-        // up to majority of Elders
+        // up to dg_size of Elders
         dg_size = cmp::min(len, dg_size);
-        if len < ELDER_SIZE {
+        if len < min_group_size {
             warn!(
                 "Delivery group only {:?} when it should be {:?}",
-                len, ELDER_SIZE
+                len, min_group_size
             )
         }