Remove potentially too costly Packets::default() (#14821)

* Remove potentially too costly Packets::default()

* Fix test...

* Restore Packets::default()

* Restore Packets::default() more

perf/src/packet.rs

@@ -11,18 +11,11 @@ pub const PACKETS_PER_BATCH: usize = 256;
 pub const NUM_RCVMMSGS: usize = 128;
 pub const PACKETS_BATCH_SIZE: usize = PACKETS_PER_BATCH * PACKET_DATA_SIZE;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Default, Clone)]
 pub struct Packets {
     pub packets: PinnedVec<Packet>,
 }
 
-//auto derive doesn't support large arrays
-impl Default for Packets {
-    fn default() -> Packets {
-        Self::with_capacity(NUM_RCVMMSGS)
-    }
-}
-
 pub type PacketsRecycler = Recycler<PinnedVec<Packet>>;
 
 impl Packets {
@@ -75,6 +68,7 @@ pub fn to_packets_chunked<T: Serialize>(xs: &[T], chunks: usize) -> Vec<Packets>
     out
 }
 
+#[cfg(test)]
 pub fn to_packets<T: Serialize>(xs: &[T]) -> Vec<Packets> {
     to_packets_chunked(xs, NUM_PACKETS)
 }