bt-bass: Standardize error type for RemoteScanStoppedOperation decode

Align RemoteScanStoppedOperation::decode to return
`UnexpectedDataLength` instead of `BufferTooSmall` when the buffer is
malformed. The former is used for these situations, and the latter is
used for encoding errors due to truncated input buffers.

Bug: 539983871
Test: cargo test

Change-Id: I94e20bdced0ed8a0dd9540e587dc3d7f695094df
Reviewed-on: https://bluetooth-review.googlesource.com/c/bluetooth/+/3320

rust/bt-bass/src/types.rs

diff --git a/rust/bt-bass/src/types.rs b/rust/bt-bass/src/types.rs
index a3d1222..b881328 100644
--- a/rust/bt-bass/src/types.rs
+++ b/rust/bt-bass/src/types.rs
@@ -87,7 +87,7 @@
     fn decode(buf: &[u8]) -> (core::result::Result<Self, Self::Error>, usize) {
         const BYTE_SIZE: usize = ControlPointOpcode::BYTE_SIZE;
         if buf.len() < BYTE_SIZE {
-            return (Err(PacketError::BufferTooSmall), buf.len());
+            return (Err(PacketError::UnexpectedDataLength), buf.len());
         }
         (Self::check_opcode(buf[0]).map(|_| RemoteScanStoppedOperation), BYTE_SIZE)
     }
@@ -1148,6 +1148,10 @@
         let (decoded, len) = RemoteScanStoppedOperation::decode(&bytes);
         assert_eq!(decoded, Ok(stopped));
         assert_eq!(len, 1);
+        assert_eq!(
+            RemoteScanStoppedOperation::decode(&[]).0,
+            Err(PacketError::UnexpectedDataLength)
+        );
     }
 
     #[test]