Log Message:
cups-filters: Make `avahi' and `dbus' support available as PKG_OPTIONS

Make `avahi' and `dbus' available as PKG_OPTIONS, both enabled by default (as
per old cups-filters).

Please note that gdbus-codegen is invoked unconditionally and so still needed
also in the `-dbus' case.

Bump PKGREVISION (strictly speaking that's probably not needed but the dbus
dependency was previously picked up indirectly via net/avahi).