v3.7.6

CHANGES:

• opam: ensure Xen bindings are built with right mirage-xen-ocaml CFLAGS (@avsm)
• opam: correctly register mirage-xen-ocaml as a depopt (@avsm)
• use mirage-protocols-3.0 interface for ipaddr printing (#408 @yomimono @linse)
• remove dependency on configurator and use dune's builtin one instead (@avsm)