sftp_attrsize: protect the macro argument with proper parentheses

src/sftp.c

@@ -94,10 +94,10 @@ static int sftp_close_handle(LIBSSH2_SFTP_HANDLE *handle);
  */
 #define sftp_attrsize(f) \
     (4 +           /* flags(4) */        \
-     ((f & LIBSSH2_SFTP_ATTR_SIZE)?8:0) +  \
-     ((f & LIBSSH2_SFTP_ATTR_UIDGID)?8:0) +                             \
-     ((f & LIBSSH2_SFTP_ATTR_PERMISSIONS)?4:0) +                        \
-     ((f & LIBSSH2_SFTP_ATTR_ACMODTIME)?8:0)) /* atime + mtime as u32 */
+     (((f) & LIBSSH2_SFTP_ATTR_SIZE)?8:0) +                             \
+     (((f) & LIBSSH2_SFTP_ATTR_UIDGID)?8:0) +                           \
+     (((f) & LIBSSH2_SFTP_ATTR_PERMISSIONS)?4:0) +                      \
+     (((f) & LIBSSH2_SFTP_ATTR_ACMODTIME)?8:0)) /* atime + mtime as u32 */
 
 /* _libssh2_store_u64
  */