Change `MessageReader` to use `with_capacity`

Some of the collections inside `MessageReader` were created with `new()`
instead of `with_capacity()` call. This patch fixes that or comments why
it was not done in some places.

src/link/mod.rs

@@ -20,6 +20,9 @@ const HEAD_UE_MESSAGE: u8 = 42;
 //  Maximum allowed size of JSON message sent from ue-server.
 const MAX_UE_MESSAGE_LENGTH: usize = 25 * 1024 * 1024;
 
+//  We do not expect to receive more that this much messages at once from ue-server
+const EXPECTED_LIMIT_TO_UE_MESSAGES: usize = 100;
+
 custom_error! { pub ReadingStreamError
     InvalidHead{input: u8}          = "Invalid byte used as a HEAD: {input}",
     MessageTooLong{length: usize}   = "Message to receive is too long: {length}",
@@ -63,8 +66,9 @@ impl MessageReader {
             reading_state: ReadingState::Head,
             read_bytes: 0,
             current_message_length: 0,
+            //  Will be recreated with `with_capacity` in `push_byte()`
             current_message: Vec::new(),
-            read_messages: VecDeque::new(),
+            read_messages: VecDeque::with_capacity(EXPECTED_LIMIT_TO_UE_MESSAGES),
             next_received_bytes: 0,
             received_bytes: 0,
         }