[image] Allow single-member archive images to be executed transparently

Provide image_extract_exec() as a helper method to allow single-member
archive images (such as gzip compressed images) to be executed without
an explicit "imgextract" step.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/image/gzip.c

@@ -163,4 +163,5 @@ struct image_type gzip_image_type __image_type ( PROBE_NORMAL ) = {
 	.name = "gzip",
 	.probe = gzip_probe,
 	.extract = gzip_extract,
+	.exec = image_extract_exec,
 };

src/image/zlib.c

@@ -159,4 +159,5 @@ struct image_type zlib_image_type __image_type ( PROBE_NORMAL ) = {
 	.name = "zlib",
 	.probe = zlib_probe,
 	.extract = zlib_extract,
+	.exec = image_extract_exec,
 };