ebtables: update to latest git 2018-05-15

66a9701 ebtables: Fix build errors and warnings
9fff3d5 include: Fix musl libc compatibility
b1cdae8 extensions: Add string filter to ebtables

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>
(backported from ac70ac3532)
(rebased patches)
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/network/utils/ebtables/patches/200-fix-extension-init.patch

@@ -247,3 +247,14 @@
  {
  	ebt_register_table(&table);
  }
+--- a/extensions/ebt_string.c
++++ b/extensions/ebt_string.c
+@@ -310,7 +310,7 @@ static struct ebt_u_match string_match =
+ 	.extra_ops	= opts,
+ };
+ 
+-void _init(void)
++__attribute__((constructor)) static void extension_init(void)
+ {
+ 	ebt_register_match(&string_match);
+ }