Add inline attribute to BytesMut::set_len (#408)

src/bytes_mut.rs

@@ -475,6 +475,7 @@ impl BytesMut {
     ///
     /// assert_eq!(&b[..], b"hello world");
     /// ```
+    #[inline]
     pub unsafe fn set_len(&mut self, len: usize) {
         debug_assert!(len <= self.cap, "set_len out of bounds");
         self.len = len;