CHANGELOG: Mention libxl blktap/tapback support

Add entry for backendtype=tap support in libxl.  blktap needs some
changes to work with libxl, which haven't been merged.  They are
available from this PR: xapi-project/blktap#394

Signed-off-by: Jason Andryuk <[email protected]>
Acked-by: Oleksii Kurochko <[email protected]>

Author: Jason Andryuk

CHANGELOG.md

@@ -26,6 +26,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
      for IPIs and Physical addressing mode for external interrupts.
  - Add a new 9pfs backend running as a daemon in dom0. First user is
    Xenstore-stubdom now being able to support full Xenstore trace capability.
+ - libxl support for backendtype=tap with tapback.
 
 ### Removed
 - caml-stubdom.  It hasn't built since 2014, was pinned to Ocaml 4.02, and has