Include arpa/inet.h to get the htonl(3) definition

MFC after: 2 weeks
Reported by: clang
Sponsored by: EMC / Isilon Storage Division

sys/cddl/boot/zfs/lz4.c

@@ -34,6 +34,8 @@
  * $FreeBSD$
  */
 
+#include <arpa/inet.h>
+
 static int LZ4_uncompress_unknownOutputSize(const char *source, char *dest,
 					    int isize, int maxOutputSize);