acl: add missing byteswap header for musl

On glibc this builds fine; on musl the byteswap header doesn't seem to be
included properly. This change adds it, fixing the build.

Type: fix
Change-Id: I402812409395d471357b6317084774afba39548f
Signed-off-by: Eric Sun <esun@meraki.com>
Signed-off-by: Pierre Pfister <ppfister@cisco.com>

src/plugins/acl/acl_test.c

@@ -18,6 +18,8 @@
  *------------------------------------------------------------------
  */
 
+#include <byteswap.h>
+
 #include <vat/vat.h>
 #include <vlibapi/api.h>
 #include <vlibmemory/api.h>