Make GNU tar ignore the apk-tools header fields

This should problably not be upstreamed

diff --git a/src/xheader.c b/src/xheader.c
index 1347ce1..89b3a44 100644
--- a/src/xheader.c
+++ b/src/xheader.c
@@ -1777,5 +1777,8 @@ struct xhdr_tab const xhdr_tab[] = {
      they are restored *only once* during extraction later on. */
   { "SCHILY.xattr", xattr_coder, xattr_decoder, 0, true },
 
+  /* Ignore apk-tools headers */
+  { "APK-TOOLS", dummy_coder, dummy_decoder, 0, true },
+
   { NULL, NULL, NULL, 0, false }
 };