qapi: Enforce feature naming rules

Feature names should use '-', not '_'.  Enforce this.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210323094025.3569441-24-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

scripts/qapi/expr.py

@@ -213,7 +213,7 @@ def check_features(features, info):
         check_keys(f, info, source, ['name'], ['if'])
         check_name_is_str(f['name'], info, source)
         source = "%s '%s'" % (source, f['name'])
-        check_name_lower(f['name'], info, source, permit_underscore=True)
+        check_name_lower(f['name'], info, source)
         check_if(f, info, source)